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Title Development of Caged Phosphine Ligands for Transition Metal Catalysis

Author(s) 小西, 菖太

Citation 北海道大学. 博士(理学) 甲第13276号

Issue Date 2018-06-29

DOI 10.14943/doctoral.k13276

Doc URL http://hdl.handle.net/2115/71328

Type theses (doctoral)

File Information Shota_Konishi.pdf

Hokkaido University Collection of Scholarly and Academic Papers : HUSCAP

https://eprints.lib.hokudai.ac.jp/dspace/about.en.jsp

Development of Caged Phosphine Ligands

for Transition Metal Catalysis

Shota Konishi

2018

Table of Contents

GENERAL INTRODUCTION 1

CHAPTER 1 18 C-8 Selective C–H Borylation of Quinolines Catalyzed by Silica-Supported Caged

Trialkylphosphosphine–Iridium Complex

CHAPTER 2 46 Synthesis, Coordination Property and Reactivity of Silica-Supported Triptycene-type

Phosphine

CHAPTER 3 74 Synthesis, Properties and Catalytic Appligcation of Borate-containing Triptycene-Type

Phosphine

PUBLICATION LIST 102

ACKNOWLEDGEMENT 104

1

General Introduction

1. Phosphorus Ligands for Transition Metal Catalysis

1.1. Introduction

Trivalent phosphorus compounds are widely used as ancillary ligands in transition metal

catalysts (Figure 1). They strongly coordinate to many transition metals to form complexes.

Ligands on the transition metal catalysts greatly influence their reactivity by changing

electronic and steric conditions1. Therefore, ligand design is important for producing highly

active catalysts and for developing new reactions.

PX

XX

M

Figure 1. Coordination of trivalent phosphorus compounds

1.2. Electronic Parameters of Phosphorus Ligands

Parameters to judge the electron donating ability of the ligands are reported.

Strohmeier and Müller reported that wave numbers of A1 stretching vibration of CO (νCO) in IR spectrum of the 1:1 type complex Ni(CO)3(PX3) synthesized from a phosphorus ligand

and Ni(CO)4 correlate to the donor ability (Figure 2a)2. The parameter was further developed

by Tolman3. Ligands with stronger donating ability have stronger back donations from Ni to

CO, which weaken CO bonds, showing lower νCO value. This value of νCO is called Tolman Electronic Parameter. Values for representative phosphorus ligands are shown in Figure 2c.

Donor abilities of phosphines also correlate to the 1JP–Se coupling constant of

corresponding phosphine selenide on 31P NMR (Figure 2b)3,4. However, the 1JP–Se value is

influenced by steric factors. Thereby, applicability of this method is limited.

2

(a) (c)

X PNi

XX

OCOC

CO

LPtBu3

PEt3P(4-MeO-C6H4)3

P(4-Me-C6H4)3

P(2-Me-C6H4)3

P(4-F-C6H4)3

νco (cm-1)2056.12061.72066.12066.72066.62071.3

1JP-Se (Hz)687684714720706743

(b)

XPXX

Se

Figure 2. (a) Nickel–Phosphine 1:1 type complex Ni(CO)3(PX3). (b) Phosphine selenides (c)

Tolman electronic parameter (νCO) and 1JP–Se coupling constant of representative phosphines.

1.3. Steric Parameters of Phosphorus Ligands

Bulkiness of the ligand is a factor that influences not only a steric environment around

the metal but also dissociation equilibrium of the ligand. Tolman proposed an index called

“cone angle” to compare bulkiness of phosphorus ligands. Cone angle is calculated using a

space-filling model of phosphorus ligands. Tolman defined cone angle as "apex angle of a

cylindrical cone, centered 2.28 Å from the center of the P atom, which just touches the van

der Waals radii of the outermost atoms of the model"5. Cone angle of PX1X2X3 can be

measured as indicated in Figure 3 and Eq 1, by using a model to minimize the sum of

half-angles.

P

2.28 Åθ1/2

θ2/2

θ3/2

Figure 3. Method of measuring cone angles for phosphine ligands.

3

2. Design of Highly Active Palladium Catalysts for Cross-coupling reactions

Pd-catalyzed cross-coupling reactions are useful reactions capable of forming

carbon-carbon and carbon-heteroatom bonds from aryl halides and various nucleophiles.

Early Pd-catalyzed cross-coupling reactions did not proceed efficiently with aryl chlorides,

which are poor in reactivity as compared with aryl bromides or iodides. A remarkable

development of the ligand enabled the reaction of aryl chloride. In 1998, Fu and co-workers

reported that the combination of PtBu3 and palladium efficiently catalyze Suzuki–Miyaura

coupling of aryl chlorides6. In the same year, Buchwald and co-workers reported that

o-(dialkylphosphino)biphenyl derivatives are also effective7. Since these breakthroughs,

various Pd catalysts capable of cross-coupling reaction of aryl chlorides have been reported.

Herein, the development of phosphorus ligands to produce highly active Pd catalysts is

shown by taking the Suzuki–Miyaura coupling reaction of aryl chloride as an example.

2.1. Alkylphosphines for Pd-catalyzed cross-coupling

These days, bulky and electron donating alkyl phosphines became common ligands for

producing highly active palladium catalysts. The high electron donating ability increases the

electron density of Pd (0) to promote rate-limiting oxidative addition (Scheme 1). In addition,

it was found by computational8 and experimental methodology9 that the formation of

coordinatively unsaturated Pd(0):P = 1:1 complex is important for the oxidative addition

process of aryl chloride. Bulkiness of the ligand is favorable for the formation of Pd(0):P =

1:1 complex because excess coordination is suppressed.

(1)

4

Scheme 1. The mechanism of palladium catalyzed Suzuki-Miyaura cross-coupling of

chloroarenees. R3P Pd PR3

R3P Pd

– PR3

R3P PdCl

ArR3P Pd

Ar'

Artransmetallation

oxidativeaddition

reductiveelimination

Ar'B(OH)2base

BX3MCl

Ar–ClAr–Ar'

2.1.1. Tri-tert-butylphosphine

Fu et al. reported that tri-tert-butylphosphine is an effective ligand for Suzuki–Miyaura

coupling catalyzed by Pd catalyst. Tri-tert-butylphosphine has bulky tert-butyl group on

phosphorus atom, which not only increase donor ability but also prevent overcoordination.

This catalyst can promote the coupling reaction even with electron deficient or rich aryl

chloride (scheme 2).

Scheme 2. Suzuki-Miyaura coupling of chloroarene with tri-tert-butylphosphine.

PMe Cl (HO)2B MePd2(dba)3 (1.5 mol%)PtBu3 (3.6 mol%)

Cs2CO3 (2 equiv.)dioxane, 80 ºC, 5 h1.05 equiv. 86% PtBu3

2.1.2. Buchwald-type biarylphosphines

In 1998, Buchwald found that a Pd catalyst with biarylphosphine L1 caused Suzuki

–Miyaura coupling of aryl chloride at room temperature. After that, Buchwald and colleagues

have developed various biarylphosphine derivatives widely used for various coupling

reactions (scheme3).

5

Scheme 3. Suzuki-Miyaura coupling of chloroarene with L1

PCy2Me2NMe Cl (HO)2B Me

Pd(OAc)2 (2 mol%)L1 (3 mol%)

CsF (3 equiv.)dioxane, rt, 19-30 h1.5 equiv. 94%

L1

Figure 4 shows features of these ligands. The bulky alkyl substituents on the phosphorus

atom increase the electron-donating ability of the ligand. Formation of a 1:1 complex with Pd

is also preferred due to its bulkiness. The aryl group at the ortho position interacts with Pd to

stabilize the complex and promote reductive elimination (figure 4).

PR2R1 R2

R3

large R · enhance rate of reductive elimination· promote Pd(0)–L 1:1 complex

electron donating alkyl groups · increase rate of oxiative addition

lower aryl ring· allows stabilizing Pd-arene interaction· promotes reductive elimination

R1,R2

· prevents cyclometallation,increase stability

Figure 4. Schematic illustration of the features of o-biarylphosphines

2.2. Triarylphosphines for Pd-catalyzed cross coupling

Triarylphosphines are moderately electron donating. Although they are generally not

effective in palladium-catalyzed cross coupling of aryl chloride, Fu et al. found the bulky

phosphine L2 is effective ligand for Suzuki-Miyaura coupling of chloroarenes (scheme 4).10

This example indicates strong electron donor ability is not an essential factor.

Scheme 4. Suzuki-Miyaura coupling of chloroarene with L2

Fe

PPh2SiMe3Me Cl (HO)2B Me

Pd2(dba)3 (1.5 mol%)L (6 mol%)

K3PO4 (2.4 equiv.)toluene70 ºC, 24 h

Me1.1 equiv.

Me87% L2

2.2.1. Bowl-Shaped Phosphines

Bowl-shaped phosphines have bulky substituents at the periphery of the phosphine.11a

The steric hindrance in the vicinity of the coordination point is small, while it has large cone

angle. Because of steric repulsion, this ligand suppresses excessive coordination with respect

6

to metals and preferentially forms a 1:1 complex with a metal11b. Tsuji reported that the

ligand L3 is effective for Suzuki–Miyaura coupling of aryl chlorides despite triarylphosphine

(Scheme 5)11c.

Scheme 5. Suzuki-Miyaura coupling of chloroarene with the bowl-shaped phosphine.

Me Cl (HO)2B Me

Pd2(dba)3·CHCl3 (1 mol%)L3 (1 mol%)

KF (3 equiv.)THF50 ºC, 15 h1.5 equiv.

88%

P

3

Me

MeMe

Me

Me

MeMe

Me

P

R1

R1

R1

R1

R2

R2

3Bowl-shaped phosphinesL3

2.2.2. Triarylphosphines with dendritically arranged tetraethylene glycol moieties

Tsuji synthesized a triarylphosphine (L4, scheme 6) whose periphery was dendritically

functionalized with tetraethylene glycol (TEG) moiety12. The Pd catalyst with L4 is effective

for Suzuki-Miyaura coupling of aryl chlorides in THF (scheme 6). It is considered that

coordinatively unsaturated catalytically active species are generated due to the steric size

around the ligand.

7

Scheme 6. Suzuki-Miyaura coupling of chloroarene with L4.

Me Cl (HO)2B Me

[PdCl2(PhCN)2] (0.1 mol%)L4 (0.2 mol%)

K2CO3 (2 equiv.)THF, 60 ºC, 20 h2 equiv. 93%

P

O

O

O

O

O

O

O

O

O

Me(OC2H4)4O

Me(OC2H4)4O

O(C2H4O)4Me

O(C2H4O)4Me

O(C2H4O)4Me

O(C2H4O)4MeO(C2H4O)4MeMe(OC2H4)4O

Me(OC2H4)4O

Me(OC2H4)4O

Me(OC2H4)4O O(C2H4O)4Me

Me(OC2H4)4O

Me(OC2H4)4O

O(C2H4O)4Me

O(C2H4O)4Me

O(C2H4O)4Me

O(C2H4O)4Me

L4

2.2.3. Threefold Cross-Linked Polystyrene–Triphenylphosphane Hybrids

Sawamura et al. developed heterogenious triarylphosphine ligands. A phosphine unit

was introduced as the threefold cross-linker in the polystyrene resin13. Complexation

experiments using CP/MAS solid state NMR showed that this ligand can selectively form a

1: 1 complex with Pd. In the vicinity of the triple crosslinking site part, the density of the

polymer chain is high, and it is considered that multiple coordination does not occur because

the phosphine moieties are difficult to approach each other. The Suzuki–Miyaura coupling of

4-chlorotoluene proceeded with a yield of 95% with a Pd complex having threefold

crosslinked PS-3p-TPP. On the other hand, PS-2p-TPP with two-point crosslinking

PS-1p-TPP with a single point grafting gave only 52% and 6% yields, respectively. The

selective formation of 1:1 complexes by three-point-crosslinking is important for high

activity (scheme 7)

8

Scheme 7. Suzuki-Miyaura coupling of 4-chlorotoluene and phenylboronic acid with

polystyrene-crosslinking phosphines.

Me Cl (HO)2B Me

[PdCl2(PhCN)2] (1 mol%)ligand (2 mol%)

K3PO4 (3 equiv.)40 ºC, 2 h1.5 equiv.

P

tBu

tBu

tBu

PSPS

PS

PPh

tBu

tBu

PS

PS

Ph2P

tBu

PS

PS-3p-TPP. 95% PS-2p-TPP, 52% PS-1p-TPP, 6%

3. Caged Phosphorous Ligands

3.1. Features of caged molecule

This section deals with ligands having a phosphorus atom at the bridgehead position of the

cage structures. Bicyclic cage structures give caged phosphorus ligands unique features

owing to limited degree of freedom. First, steric effects and three-dimensional environment

of the ligand can easily be controlled. Second, electronic properties of the phosphorus atom

can be potentially tuned by the bridgehead atom at the side opposite to the phosphorus atom

because its location is fixed near the phosphorus atom, it can affect the reactivity of the

phosphorus atom. Examples of ligands having these features are shown below.

3.2. Sterical features of caged ligands

3.2.1. Phosphabarrelenes

Breit and co-workers developed benzophosphabarelenes via a [4+2] cycloaddition

reaction of the phosphabenzene with benzyne (scheme 8). Due to the rigid cage structure, the

substituent at the α position gives an adequate and rigid stereo environment near the central

metal14.

Scheme 8. The synthesis of L5.

P

PhMe

Me

Me

Me

P

Ph

Ar Ar

Br

F

Mg

THF, reflux

L5

9

A Rh catalyst with this ligand showed a high catalytic activity on hydroformylation of

the internal alkene without causing isomerization of the alkene (Scheme 9).

Scheme 9. Rhodium–L5-catalyzed hydroformylation of the internal alkene.

3, E/Z 77:23

OO

O

O

Rh(acac)(CO)2 (0.014 mol%)L5 (0.28 mol%)H2/CO (1:1, 10 bar)

toluene, 70 ºC

4a

4b

4c

4d4a : 4b : 4c : 4d = 0 : 57.6 : 35.7 : 0

3.2.2. Bicyclic Phosphites

Caged phosphites with a [2.2.2]-fused structure are synthesized by Verkade, Reynolds et al.

(Figure 5) in 196015a. The substituents on the phosphorus are constrained in the cage structure.

As a result, this phosphorus ligand has a smaller cone angle than trimethylphosphite5.

O OPO

R

Figure 5. The structure of [2.2.2] fused bicyclic phosphites.

3.3. Effects of bridgehead atoms

3.3.1. Proazaphosphatranes

Verkade and co-workers developed proazaphosphatranes, which have a [3.3.3]-fused

triaminophosphine structure.16a The three nitrogen atoms attached to the bridgehead

phosphorus atom adopt nearly planar geometry, indicating significant donation of the N lone

pair to the phosphorus atom. The bridgehead N atom is bound at the backside of the

phosphorus atom, so that the nitrogen atom can donate electrons through a transannular

orbital interaction with the phosphorus atom (figure 6). As a result, these phosphorus

compounds show extremely high basicities and are used as organic superbases.16b These

compounds are excellent ligands for Pd-catalyzed cross-coupling of chloroarenes, such as

Suzuki–Miyaura coupling16c, Stille coupling16d, Buchwald–Hartwig amination16e and

α-arylation of nitriles16f.

10

(a) (b)

N P NN

N

RRR

NHP NN

N

RRR

Figure 6. Free (a) and protonated form (b) of proazaphosphatranes.

3.3.2. Phosphatriptycenes

A tryptycene-type molecule having phosphorus atom at the bridgehead have been

reported. Azaphosphatriptycene was reported by Hellwinkel et al. in 1969 (Figure 7a). 17a

Diphosphatriptycene (Figure 7b)17b and phosphatriptycene (Figure 7c)17c were reported in

1971 and 1974, respectively. Kawashima synthesized an oxy-functionalized

phosphatriptycene derivative (Figure 7d), This ligand has lower σ-donor property than triphenylphosphine as proved by the CO stretching vibration of the tungsten carbonyl

complex and 1JP-Se value of corresponding phosphine selenide.17d Tamao and Tsuji

synthesized various 9-sila-10-phosphatriptycene derivatives (Figure 7d). The substituents on

the bridgehead-silicon atom did not influence the σ-donor ability of the phosphines.17e

Figure 7. Examples of phosphatriptycene derivatives.

3.3.3. Silicon-constrained caged trialkylphosphines

Sawamura reported cage shaped trialkylphosphine constrained by a silicon atom.18a

Having a cage shape, it is as compact as PMe3 (figure 8a). The substituent on the silicon is

fixed to the opposite side of the lone electron pair of the bridgehead phosphorus. Substituents

at the bridgehead Si atom of the SMAP derivatives had significant impact on electron-donor

power of the P lone pair due to long range orbital interactions in the rigid cage system.

(figure 8b).18b

(a) (b) (c) (d) (e)

P

N

P

P

P

CH MeO

P

C

OMeOMeOH

P

SiR

11

(a) (b)

Si

P

X

X

4-NMe2H3,5-(CF3)2

1JP-Se(Hz)729.3735.4739.1

Figure 8. (a) Structure of SMAPs. (b) 1JP-Se coupling constants of corresponding SMAP

selenides.

3.3.4. Immobilization of caged trialkylphosphines on solid supports

3.3.4.1. Immobilization on gold surface

Caged trialkylphosphine (SMAP) immobilized on gold surface ([Au]-SMAP) was

developed by Hara, Sawamura and co-workers19. The phosphine molecules with an

alkanethiolate linkers form a self-assembled monolayer on the gold surface.

Au

Si

P

S

7

Si

P

S

7

Si

P

S

7

Figure 9. The structure of [Au]-SMAP.

The Au-SMAP–rhodium complex showed high catalytic activity to dehydrogenative

silylation of alcohols with hydrosilane(table 1). The catalyst was easy to separate from the

reaction mixture after the reaction, and could be recycled at least four times. The silylation

reaction proceeded selectively with primary alcohols in the presence of secondary alcohols.

The highly selectivity is attributed to the steric congestion of the catalytic environment,

which exists in a densely packed rhodium–phosphane assembly.

12

Table 1. [Au]-SMAP–Rh-catalyzed primary alcohol selective silylation.

Me OH

Me

Me

OH

4

4

5a

5b

[Au]-SMAP-Rh(silane/catalyst150 000:1)

Me2PhSiH, hexane25 ºC, 16 h

Me OSiMe2Ph

Me

Me

OSiMe2Ph

4

4

6a

6b

1st run2nd run3rd run4th run

yield(%)60585550

TON

90000870008300075000

6a/6b

>99.5:0.5>99.5:0.5>99.5:0.5>99.5:0.5

3.3.4.2. Immobilization on silica gel

Sawamura et al. reported a ligand in which the silicon moiety of cage type

trialkylphosphine was immobilized on silica gel.20 Since the cage-type skeleton is rigid, the

lone pair of the phosphorus atom is always fixed upward with respect to the silica surface, so

that the transition metal complex is not sterically hindered by the silica surface (Figure 10).

In addition, it was shown that silica-SMAP can selectively form a complex with Rh:P = 1:1

even though it is a compact ligand. Since the steric hindrance of the ligand is small, the

coordination unsaturated complex obtained is considered to have an open reaction space.

Si

P

OSiOO

O

OSiOO

O

SiMe3

SiO2

Si

P

OSiOO

O

[Rh] [Rh]selective

Rh:P = 1:1complexation

Figure 10. The structure of Silica-SMAP.

13

3.3.4.2.1. Silica-SMAP–Pd Catalyzed Borylation of Chloroarenes

Silica-SMAP-palladium catalyst was effective for palladium-catalyzed Miyaura borylation

reaction of aryl chlorides (Eq. 2).21 Selective formation of a Pd:P = 1:1 complex is considered

to be the key for high reactivity on the activation of C–Cl bond. Even very bulky aryl

chlorides were applicable for this catalyst system. The substrates are accessible to the

reaction center due to the very compact nature of Silica-SMAP.

ClO

BO

BO

OB

O

OSilica-SMAP (0.5 mol%)Pd(OAc)2 (0.5 mol%)

KOAc (3.0 eq), toluene110 ºC 72%

3.3.4.2.2. Silica-SMAP–Ir Catalyzed Direct Borylation of C–H bonds

In 2002, Ishiyama, Miyaura, Hartwig et al. reported direct borylation reaction of

C(sp2)–H bonds of aromatic compounds with iridium–bipyridine based catalyst.22a-b This

reaction proceeds preferentially at the C–H bonds with less steric hindrance react. Sawamura

and co-workers found that selective C–H borylation at the position ortho to the coordinative

functional groups proceed with Silica-SMAP-Ir complex (eq. 3).23a-c

DG

OB

OB

O

O

HDG = Cl, CO2Me, OCONMe2, etc.

Silica-SMAP[Ir(OMe)(cod)]2

DG

BO

O

It is proposed that triboryl iridium complex is an active species in the reaction using

Ir-bipyridine type catalyst (Figure 11a).22b On the other hand, when using monodentate

phosphine Silica-SMAP, one more vacant coordination site is formed, and cleavage of the

C–H bond and the coordination of a functional group occars at the same time, resulting in

regioselectivite reaction at the position ortho to the functional group (figure 11b).

14

(a) (b)

H

N

IrBpin

Bpin

BpinN

DG

[P]

H

IrBpin

Bpin

BpinDG

Figure 11. Proposed C–H bond activating transition states with triboryliridium complexes.

It was also found that the silica-SMAP-Ir catalyst undergoes a selective borylation reaction of

inactive C(sp3)–H bond. In 2-alkylpyridines, the primary or secondary C(sp3)–H bond located

γ to the pyridine nitrogen atom was selectively borylated (eq4).23d

N N

BOO

HOB

OBO

OSilica-SMAP[Ir(OMe)(cod)]2

4. Overview of This Thesis

The author focused on the structural feature of caged phosphine ligands. Caged

phosphine-based transition metal catalysts and its reactions were investigated. In chapter 1,

Silica-SMAP–Ir catalyst system was applied for the site-selective borylation of quinoline

derivatives. In chapter 2, synthesis and coordination property of a silica-supported

triptycene-type caged phosphine ligand and its application to Suzuki-Miyaura coupling are

described. Chapter 3 describes the synthesis of a caged phosphine containing a borate moiety

and its reactivities.

Chapter 1 describes C-8 selective direct C–H borylation of quinolines using

Silica-SMAP–iridium catalyst system. This reaction enabled direct, regioselective

introduction of the boron functional group into the quinoline ring to give various 8-quinoline

boronic acids, which can be used as versatile synthetic intermediate for 8-substituted

quinoline derivatives. This method could be used for shortened synthesis of the highly

functionalized quinoline compound, which is reported as a CRF1 receptor antagonist.

15

[Ir(OMe)(cod)]2 (2 mol% Ir)Silica-SMAP (2 mol%)

B2pin2(1.0 equiv)tBuOMe60 °C, 12 h

NMeO Me

N

NMeO Me

N

NMeO Me

N

Bpin87%

CRF1 recepterantagonist

Cl

H

Chapter 2 describes Silica-TRIP with cageed triarylphosphine immobilized on silica. The

complexation behavior of Silica-TRIP ligand with Pd was analyzed. Silica-TRIP was used for

complexation with a Pd complex and the resulting complex was analyzed by solid state 31P

CP/MAS NMR. The Pd:P = 1:1 type complex was selectively formed even when excess

Silica-TRIP was applied. Silica-TRIP found out to be effective ligand to promomote the

Pd-catalyzed cross-coupling between arylchlorides and arylboronic acids. The reaction did

not proceed in the corresponding homogeneous ligand.

SiO2

OSiOO

O

P

SiOSiOO

O

SiMe3

Silica-TRIP

Chapter 3 describes synthesis, property and catalytic application of a triptycene-type

anionic borate-phosphine ligand L-X (X = Na or NBu4). A negative charge at the bridgehead

boron atom affected the donor-power of the phosphorus center. The coordination property of

L-X to [PdCl(η3-allyl)] was dependent on the counter cation, giving a neutral Pd complex

[PdCl(η3-allyl)(L-NBu4)] from L-NBu4 in CH2Cl2 or a zwitterionic Pd complex

[Pd(η3-allyl)(MeCN)(L)] from L-Na in MeCN/CH2Cl2. Utility of L-X as a ligand for metal catalysis was demonstrated in the Pd-catalyzed Suzuki–Miyaura cross-coupling of aryl

chlorides.

P

B

X

16

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Urgaonkar, S.; McLaughlin, P. A.; Verkade, J. G. J. Am. Chem. Soc. 2004, 126,

16433–16439. (e) Urgaonkar, S; Verkade, J. G. Org. Lett. 2003, 5, 815–818. (f) You, J.;

Verkade, J. G. Angew. Chem. Int. Ed. 2003, 42, 5051 –5053.

17

(17) (a) Hellwinkel, D.; Schenk, W. Angew. Chem. Int. Ed. 1969, 8, 987–988. (b) Weinberg,

K. B.; Whipple, E. G. J. Am. Chem. Soc. 1971, 93, 1801–1802. (c) Jongsma, C.; De

Kleijn, J. P.; Bickelhaupt, F. Tetrahedron 1974, 30, 3465. (d) Kobayashi, J.; Agou, T.;

Kawashima, T. Chem Lett 2003, 32, 1144–1145. (e) Tsuji, H.; Inoue, T.; Kaneta, Y.;

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Ochida, A.; Ito, S.; Miyahara, T.; Ito, H.; Sawamura, M. Chem. Lett. 2006, 35, 294–295.

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18

Chapter 1

C-8 Selective C–H Borylation of Quinolines Catalyzed by Silica-Supported Caged Trialkylphosphosphine–Iridium

Complex

NMeO

N

Me

[Ir(OMe)(cod)]2(2 mol% Ir)Silica-SMAP(2 mol% P)

pinB–BpinMTBE, 60 ºC

NMeO

N

MeBpin

Si

P

Silica-SMAP

SiO

OO

O

SiMe3

C-8-Selective C–H Borylation

H 1

35

6

8SiO

OO

O

Site-selective C–H borylation of quinoline derivatives at the C8 position has been

achieved by using a heterogeneous Ir catalyst system based on a silica-supported cage-type

monophosphine ligand Silica-SMAP. The efficient synthesis of a corticotropin-releasing

factor 1 (CRF1) receptor antagonist based on a late-stage C–H borylation strategy

demonstrates the utility of the C8 borylation reaction.

19

1. Introduction

The quinoline heterocyclic scaffold is an important structural motif that is found in many

natural products, bioactive compounds, dyes, and other functional molecules, for example,

Alq3 for OLEDs.1-3 Accordingly, the development of efficient methods for accessing

substituted quinolines is a subject of considerable importance. In particular, streamlining the

synthetic process through the introduction of site selective direct functionalization of a

quinoline C–H bond is highly desirable. Several methods that allow direct C–C bond

formation at the C2 position of quinolines or quinoline N-oxides, using Rh,4 Pd,5 Ni,6 Cu,7

and Ag8 catalyst systems, have been reported in recent years. The C2 selectivity of these

catalysts is based on the inherent reactivity of the C=N bond or the N-adjacent C–H bond. In

contrast, site-selective catalytic C–H transformation at the C8 position was only reported by

Chang and coworkers. In their work, Rh–NHC (NHC = N-heterocyclic carbene) catalytic

systems were used for C8 arylation with aryl bromides.9–10

Miyaura, Ishiyama, and co-workers reported that direct C–H borylation of quinoline

occurred preferentially at the C3 position when an Ir–bipyridine-type (Ir–dtbpy;

Hartwig–Ishiyama–Miyaura catalyst; dtbpy = 4,4-di-tert-butylbipyridine) catalyst was used,

with a large excess of the quinoline substrate (10 equiv).11 More recently, Marder and

co-workers provided guidelines for achieving selective borylation at the C3, C4, C6, or C7

positions of disubstituted quinolines.12 In contrast, access to the much desired

quinoline-8-boronic acid has required multiple steps, which involve generation of the

corresponding halide as an immediate precursor.13

In this chapter, Ir-catalyzed site-selective C–H borylation of quinoline derivatives with

bis(pinacolato)diboron (pinB–Bpin, 2) is described. C8-selective borylation was effected by

choosing silica-supported trialkylphosphine (Silica-SMAP) as a monodentate P ligand for

Ir.14–16 The borylation reaction proceeded under mild reaction conditions with excellentsite

selectivity toward various substrates with different substitution patterns.

2. Results and Discussion

The reaction of quinoline 1a (0.30 mmol) and diboron 2 (1.1 equiv) in methyl

tert-butyl ether (MTBE) in the presence of an immobilized catalyst precursor (Ir, 2 mol%),

prepared in situ from Silica-SMAP, and [Ir(OMe)(cod)]2 (P/Ir, 1:1; cod =

cycloocta-l,5-diene) proceeded at 60 ºC over 12 h with 94% consumption of 1a (Scheme 1).

The 1H NMR spectrum of the crude product indicated that the major product was

C8-borylated quinoline 3a, which was contaminated with small amounts of reduced products,

such as 1,2,3,4-tetrahydroquinoline (4a, 13% yield, analysis based on 1H NMR

20

spectroscopy).17 As the quinoline-8-boronic acid pinacol ester (3a) was unstable to

hydrolysis,18 the crude product was subjected to oxidation with NaBO3·4H2O, followed by

treatment with (Boc)2O (Boc = tert-butoxycarbonyl). This method afforded

O-tert-butoxycarbonyl-8-hydroxyquinoline (6a) in 68% yield after purification by silica-gel

chromatography. No other isomers were detected in the crude reaction mixture.

Scheme 1. Silica-SMAP–Ir catalyzed C–H borylation of quinoline.

[Ir(OMe)(cod)]2 (2 mol% Ir)Silica-SMAP(2 mol%)

MTBE60 ºC, 12 h

2 (1.1 eq)

1a

3a

N

NBpin

1) NaBO3•4H2O (3 eq) THF/H2O (1:1) rt, 3 h2) (Boc)2O (2 eq) DMAP (0.1 eq) THF, rt, 1 h

NOBoc6a (68%)–HBpin (5)

B BO

OO

O

NH

4a (13%)

Based on the fact that the reaction of 2-substituted quinolines (see below) proceeded with

exclusive selectivity, we assumed that Ir-catalyzed addition of the pinBH (5) byproduct

across the C=N bond (hydroboration) of 1a triggered reductive side reactions.19 In fact, the

reaction of 1a with 5 (1.1 equiv) instead of 2, under otherwise identical conditions, produced

the C8-borylated product 3a in only 17% yield, while giving the reduced product 4a in an

increased yield of 30% with 67% conversion of 1a (analysis based on 1H NMR

spectroscopy).

The selective borylation at the C8 position is thought to be due to coordination of the

ring nitrogen atom to the Ir catalyst center. This contrasts with previous directed (hetero)

arene C–H borylation using Silica-SMAP, which required pendant functional groups as

coordination-based directing moieties.14c–e, g The Ir center is most likely mono-P ligated and

in a monomeric form because of the geometrical constraint of the directional phosphine

molecule (SMAP) that is immobilized on the solid surface in a site-isolated fashion. Thus,

C–H bond cleavage should occur through a four-membered iridacyclic reaction pathway. The

corresponding Rh catalyst (Silica-SMAP/[Rh(OMe)(cod)]2) did not yield the C8-borylated

product (3a) with 60% consumption of 1a under otherwise identical conditions, and instead

gave a complex mixture containing the tetrahydroquinoline 4a in 6% yield. The Ir-catalyzed

borylation of 1a did not proceed efficiently with other phosphine ligands shown in Figure 1.

The use of silica-supported triarylphosphane ligand (Silica-TRIP),20 a

threefold-benzannulated analogue of Silica-SMAP, gave only a trace of 3a. Homogeneous

monodentate phosphine ligands such as Ph-SMAP,21 PMe3, PBu3, PCy3, PtBu3, PPh3, and

21

XPhos (XPhos=2-dicyclohexylphosphino- 2’,4’,6’-triisopropylbiphenyl) induced no reaction

or only trace reactions. No reaction occurred when a phosphine-free Ir system was used.

These ligand effects indicate the crucial importance of both the SMAP structure and its

immobilization on a solid surface. The method using the Silica–SMAP–Ir system was

broadly applicable to substituted quinolines. The results of borylation of monosubstituted

quinolines are summarized in Table 1.

OSiOO

O

SiMe3OSiOO

O

P

Si

SiO2

Silica-TRIP

Si

P

Ph-SMAP

PMe3PBu3PCy3PtBu3PPh3none

PCy2iPr iPr

iPrXphos

Figure 1. The ligands induced trace of no reaction.

C2 substituted substrates generally resulted in very clean C(8)–H borylation reactions

without giving reduced side products. For example, 2-methylquinoline (1b, quinaldine) was

converted into 8-borylquinaldine (3b) in 99% yield (86% yield after purification) without

formation of a reduced heterocyclic compound (4) (Table 1, entry 1). In contrast, the reaction

of 1b with the Ir–dtbpy catalyst system gave the C4, C6, and C7 borylation products in 16%,

27%, and 20% yields, respectively, along with diborylation products.11,12 It was possible to

reduce the catalyst loading of the Silica–SMAP–Ir system to 0.05 mol% (Ir) upon scaling up

this transformation (Table 1, entry 2). C8 borylation also proceeded cleanly, even with the

sterically more demanding nPr group (1c) at the C2 position (Table 1, entry 3). Furthermore,

substitution with methoxy (1d) or N,N-diethylamino (1e) groups at the terminus of the C2

pendant chain was tolerated (Table 1, entries 4 and 5). In contrast, monosubstitution with Me

or MeO groups at the C3 (1f), C4 (1g), and C6 (1h) positions, leaving the C2 position

unsubstituted, did not cause a significant effect on the reaction profile of the parent quinoline

1a (Table 1, entries 6–8).22 These results strongly support the above-mentioned assumption

that the C2 substituents blocked the undesired C=N reduction with 5.

22

Table 1. Silica-SMAP-Ir catalyzed borylation of monosubstituted quinolines.a

entry substrate product temp. (ºC) yield (%)

1

2d 1bN Me

3bN Me

Bpin

50

80

86b (99)c

91b (99)c

3 1cN nPr

3cN nPr

Bpin

50 80b (99)c

4 1dN OMe

5

3dN

Bpin

OMe5

50 74b (88)c

5

1eN

NEt25

3eN

Bpin

NEt25

50 81b (99)c

6

1fN

Me

6fN

OBoc

Me

60 61e

7

1gN

Me

6gN

OBoc

Me

60 71e

8

1hN

MeO

6hN

OBoc

MeO

60 60e

a The reaction was carried out with 1 (0.30 mmol), 2 (0.33 mmol), [Ir(OMe)(cod)]2 (1 mol%)

and Silica-SMAP (2 mol%) in MTBE (1.5 mL) for 12 h. Yields of purified boronates (3) are

shown in parentheses. b Yield of isolated C8-borylated product 3. c Yield of 3, as determined

by 1H NMR spectroscopy of the crude product. d 1b (6 mmol), 2 (6.6 mmol), [Ir(OMe)(cod)]2

(0.025 mol%), and Silica-SMAP (0.05 mol%) in MTBE (1.5 mL), at 80 ºC for 12 h. e Yield

of the isolated O-tert-butoxycarbonyl-8-hydroxyquinoline 6.

23

The results of C8 borylation of mono- or disubstituted quinaldines (di- or trisubstituted

quinolines) are summarized in Table 2. Reflecting the substituent effect at the 2-position,

these substrates were converted cleanly into the corresponding C8 borylation products in high

yields. Ring substitution with chlorine (Table 2, entries 1, 3, 6) or Boc-protected oxygen

atoms (Table 2, entry 4) was not detrimental to the reaction. Importantly, the steric effects of

substituents (Me, MeO, Cl) at the adjacent C7 position did not hamper C8 borylation (Table 2,

entries 6–8).

Table 2. Silica-SMAP-Ir-catalyzed borylation of di- or trisubstituted quinolines.a

entry substrate product temp. (ºC) yield (%)b

1

1iN Me

Cl

3iN Me

Bpin

Cl

60 81 (94)

2

1jN Me

Me

3jN Me

Bpin

Me

50 86 (99)

3

1kN Me

Cl

3kN Me

Bpin

Cl

60 79 (91)

4

1lN Me

BocO

3lN Me

Bpin

BocO

50 76c

5

1mN Me

Ph

3mN Me

Bpin

Ph

60 71 (86)

6d 1n

N MeCl 3n

N MeBpin

Cl

60 84 (96)

7

1oN MeMeO

3oN Me

BpinMeO

50 86 (92)

24

8

1pN MeMe

Me

3pN Me

BpinMe

Me

50 84 (99)

a The reaction was carried out with 1 (0.30 mmol), 2 (0.33 mmol), [Ir(OMe)(cod)]2 (1 mol%)

and Silica-SMAP (2 mol%) in MTBE (1.5 mL) for 12 h. Yields of purified boronates (3) are

shown in parentheses. b Yields of the purified boronates (3). Yields of 3 based on 1H NMR

analysis of crude products are shown in parentheses. c Yield of isolated arylation product 9l.

As the boronate 3l was unstable, it was transformed into 9l through Suzuki–Miyaura coupling

with methyl 4-bromobenzoate under the conditions described in Scheme 2. d One equivalent

of 2 was employed.

The molecular structure of 3n was determined by single crystal X-ray diffraction

analysis (Figure 2). No intra- or intermolecular interaction between the N lone pair and the

boron atom was found in the solid-state structure.

Figure 2. Molecular structure of 3n.

25

The reaction of 2,3-dimethylquinoxaline (1q) with 2.2 equivalents of 2, catalyzed by the

Silica–SMAP–Ir system, afforded the 5,8-diborylation-product 3q in 62% yield, as shown in

eq 1. The quinoxaline heterocyclic scaffold is a versatile structural motif found in various

functional molecules with potential applications in the development of electronic and

luminescent devices.23

1q 3qN

N

Me N

N

MeBpin

Me MeBpin

[Ir(OMe)(cod)]2 (2 mol% Ir)Silica-SMAP(2 mol%)

MTBE60 ºC, 12 h

B BO

OO

O

pinB Bpin, 2(2.2 eq)

(1)

62% (isolated)

The C8-borylated quinaldine 3b can be used for various transformations including

oxidation,24 one-carbon-homologation/oxidation sequence,25 Rh-catalyzed Heck-type

reaction,26 and Suzuki–Miyaura coupling27 (Scheme 2). The excellent yields of these

transformations show the utility of C8-borylated quinoline derivatives as a point of structural

diversification.

Scheme 2. Transformations of the C-8 borylation product 3b.

N Me

CO2Me

N Me

CO2Bu

N MeBpin

e

3b

9b, 94%

8, 92%

d

a,b N MeOBoc

N Me

OH

6b, 92%

7, 65%

c,a

Conditions: a NaBO3·4H2O (3 eq) in THF/H2O (1:1), rt, 3 h. b (Boc)2O (2 eq), DMAP (0.1

eq) in THF, rt, 1 h. c bromochloromethane (2 eq), n-BuLi (1.7 eq) in THF, –78 °C to rt, 1 h. d

n-Butyl acrylate (5 eq), [Rh(OH)(cod)]2 (2.5 mol%) in dioxane/H2O (50:1), 90 °C, 16 h. e

Methyl 4-bromobenzoate (1.5 eq), Pd(PPh3)4 (5 mol%), K3PO4 (3 eq) in THF/H2O (5:1),

60 °C, 12 h.

26

The Silica-SMAP–Ir–catalyzed C8 Borylation showed a utility for late-stage

functionalization of quinoline ring. A corticotropin-releasing factor 1 (CRF1) receptor

antagonist (14) was synthesized based on a late-stage C–H borylation strategy, as outlined in

Scheme 3.28 Commercially available 3-methoxyaniline (10) was transformed into

4-chloro-7-methoxyquinaldine (11) according to the literature.29 Treatment of 11 with excess

dipropylamine in the presence of TsOH furnished 4-dipropylamino-7-methoxyquinalidine

(12) as a substrate for Ir-catalyzed C–H borylation. The reaction of 12 with one equivalent of

diboron reagent 2 in the presence of the Silica–SMAP–Ir catalyst system (2 mol%) at 60 ºC

over 12 h cleanly produced the desired C8-borylation product 13 (unpurified) with good site

selectivity. Remarkably, the C–H bonds at the C3 and C5 positions, which are proximal to

the dipropylamino group, were intact. Finally, Suzuki–Miyaura coupling between the

boronate 13 and 4-bromochlorobenzene gave the CRF1 receptor antagonist 14 (57% yield

from 12). The highly functionalized boronate 13 has the potential to be a versatile precursor

for analogous 8- substituted quinoline derivatives.

Scheme 3. Synthesis of CRF1 receptor antagonist based on a late-stage C–H borylation

strategy.

N Me

N

MeO

Cl

N Me

N

MeOBpin

N Me

N

MeON MeMeO

Cl

MeO NH2

3 steps

11 27%

TsOH•H2O (1.7 eq)

n-Pr2NH(excess)

[Ir(OMe)(cod)]2(2 mol% Ir)Silica-SMAP(2 mol%)

2 (1.1 eq)MTBE60 ºC, 12 h

Pd(PPh3)4(5 mol%)4-Br-C6H4Cl(1.5 eq)

K3PO4 (3 eq)THF/H2O (5:1)60 ºC, 15 h

12 82%

14 57% from 12

CRF1 receptor antagonist

10

13

27

3. Conclusion

A heterogeneous Ir catalyst system based on the silica-supported cage-type

monophosphane ligand Silica-SMAP enabled catalytic site-selective C–H borylation of

quinolines at the C8 position, thereby complementing existing quinoline borylation methods

using Ir–bipyridine-type catalysts. The synthesis of a CRF1 receptor antagonist based on a

late-stage C–H borylation strategy demonstrated the utility of the C8 borylation.

4. Experimental Section

4.1. Instrumentation and Chemicals 1H (300 MHz) and 13C (75.4 MHz) NMR spectra were recorded on a Varian Gemini 2000

spectrometer. 11B (128 MHz) NMR spectra were recorded on a JEOL JNM-ECA

spectrometer. Chemical shift values for 1H, 13C and 11B are referenced to Me4Si, the residual

solvent resonances and BF3•OEt2, respectively. Chemical shifts are reported in δ ppm.

High-resolution mass spectra were recorded on a Thermo Fisher Scientific Exactive, JEOL

JMS-T100LP mass spectrometer or JEOL JMS-T100 GC mass spectrometer at the

Instrumental Analysis Division, Equipment Management Center, Creative Research

Institution, Hokkaido University. TLC analyses were performed on commercial glass plates

bearing 0.25-mm layer of Merck Silica gel 60F254. Silica gel (Kanto Chemical Co., Silica gel

60 N, spherical, neutral) was used for column chromatography. GLC analyses were

conducted on a Shimadzu GC-14B equipped with a flame ionization detector. Melting points

were determined on a micro melting point apparatus (Yanaco: MP-500D) using micro cover

glass.

All reactions were carried out under a nitrogen atmosphere. Materials were obtained from

commercial suppliers or prepared according to standard procedures unless otherwise noted.

[Ir(OMe)(cod)]2 was prepared according to the literature.30 Ph-SMAP,21c Silica-SMAP14b and

Silica-TRIP20b were prepared with CARiACT Q-10® according to the reported procedure.

CARiACT Q-10 (Catalyst grade, 75-150 µm) was purchased from Fuji Silysia Chemical Ltd.

and dehydrated by heating at 150 ˚C for 10 h and stored in a glove box before use. All

solvents for catalytic reactions were degassed via four freeze–pump–thaw cycles before use.

Bis(pinacolato)diboron (2) was purchased from AllyChem Co., Ltd., and recrystallized from

pentane before use.

4.2. Experimental Procedures

Typical Procedure for the Borylation of Quinoline (1a) with Immobilized Ligands

(Scheme 1). In a glove box, Silica-SMAP (0.070 mmol/g, 85.7 mg, 0.006 mmol, 2 mol%),

28

bis(pinacolato)diboron (2) (83.8 mg, 0.33 mmol), and anhydrous, degassed MTBE (0.5 mL)

were placed in a 10-mL glass tube containing a magnetic stirring bar. A solution of

[Ir(OMe)(cod)]2 (2.0 mg, 0.003 mmol, 1 mol%) in MTBE (1 mL), and quinoline (1a) (38.7

mg, 0.3 mmol) were added successively. The tube was sealed with a screw cap and removed

from the glove box. The reaction mixture was stirred at 60 ºC for 12 h, and filtered through a

glass pipette equipped with a cotton plug. Solvent was removed under reduced pressure. An

internal standard (1,1,2,2-tetrachloroethane) was added to the residue to determine the yield

of the product 3a by 1H NMR (51%). Next, the crude product (3a) and sodium perborate

tetrahydrate (139 mg, 0.9 mmol) were added to a 10-mL glass tube containing a magnetic

stirring bar, and the mixture was dissolved in a solution of THF (1.5 mL) and water (1.5 mL).

The reaction mixture was stirred vigorously at room temperature for 3 h under air. The

volatiles were removed under reduced pressure. Next, THF (3 mL), di-tert-butyl dicarbonate

(131 mg, 0.6 mmol), and 4-(N,N’-dimethylamino)pyridine (3.7 mg, 0.03 mmol) were added

successively to the tube. The reaction mixture was stirred for 1 h at room temperature.

Solvent was removed under reduced pressure. The residue was then purified by silica gel

chromatography to give 6a (50.0 mg, 0.20 mmol in 68% isolated yield based on 1a).

Typical Procedure for the Borylation of Quinoline (1a) with Soluble Ligands (Scheme 1).

In a glove box, bis(pinacolato)diboron (2) (83.8 mg, 0.33 mmol) and anhydrous, degassed

MTBE (0.18 mL) were placed in a 10-mL glass tube containing a magnetic stirring bar. A

solution of Ph-SMAP (1.3 mg, 0.006 mmol, 2 mol%) in MTBE (0.32 mL), a solution of

[Ir(OMe)(cod)]2 (2.0 mg, 0.003 mmol, 1 mol%) in MTBE (1 mL), and quinoline (1a) (38.7


from the glove box. The reaction mixture was stirred at 60 ºC for 12 h. Solvent was removed

under reduced pressure. An internal standard (1,1,2,2-tetrachloroethane) was added to the

residue to determine the yield of the product 3a by 1H NMR (<1% yield).

Typical Procedure for the Borylation of Quinoline Derivatives (Table 1, entry 1). In a

glove box, Silica-SMAP (0.070 mmol/g, 85.7 mg, 0.006 mmol, 2 mol%),

bis(pinacolato)diboron (2) (83.8 mg, 0.33 mmol), and anhydrous, degassed MTBE (0.5 mL)

were placed in a 10-mL glass tube containing a magnetic stirring bar. A solution of

[Ir(OMe)(cod)]2 (2.0 mg, 0.003 mmol, 1 mol%) in MTBE (1 mL), and quinaldine (1b) (41.6


from the glove box. The reaction mixture was stirred at 50 ºC for 12 h, and filtered through a

glass pipette equipped with a cotton plug. Solvent was removed under reduced pressure. An

29

internal standard (1,1,2,2-tetrachloroethane) was added to the residue to determine the yield

of the product 3b by 1H NMR (99%). The crude material was purified by Kugelrohr

distillation to give 3b (67.6 mg, 0.26 mmol in 86% isolated yield).

Procedure for the Borylation of 1l and the Following Suzuki-Miyaura Coupling with

Methyl 4-Bromobenzoate (Table 2, entry 4). In a glove box, Silica-SMAP (0.070 mmol/g,

85.7 mg, 0.006 mmol, 2 mol%), bis(pinacolato)diboron (2) (83.8 mg, 0.33 mmol), and

anhydrous, degassed MTBE (0.5 mL) were placed in a 10-mL glass tube containing a

magnetic stirring bar. A solution of [Ir(OMe)(cod)]2 (2.0 mg, 0.003 mmol, 1 mol%) in MTBE

(1 mL) and 1l (77.8 mg, 0.3 mmol) were added successively. The tube was sealed with a

screw cap and removed from the glove box. The reaction mixture was stirred at 50 ºC for 12

h, and filtered through a glass pipette equipped with a cotton plug. Solvent was removed

under reduced pressure. An internal standard (1,1,2,2-tetrachloroethane) was added to the

residue to determine the yield of the C-8-borylated product 3l by 1H NMR (80%). Next, the

crude product (3l), methyl 4-bromobenzoate (96.8 mg, 0.45 mmol), Pd(PPh3)4 (17.3 mg,

0.015 mmol), and K3PO4 (191 mg, 0.9 mmol) were added successively to a 10-mL

two-necked round-bottom flask containing a magnetic stirring bar under an Ar atmosphere,

and the mixture was dissolved in a solution of THF (3 mL) and H2O (0.6 mL). The reaction

mixture was stirred at 60 ºC for 12 h, and then cooled to room temperature. After addition of

water, the crude mixture was extracted with Et2O. The organic layer was washed with brine,

dried over MgSO4, filtered and concentrated. The residue was then purified by silica gel

chromatography (1:9 EtOAc/hexane) to give 9l (90.0 mg, 0.23 mmol in 76% isolated yield).

Procedure for the Oxidation of 3b and the Following Boc-Protection (Scheme 2, upper

right). Under an air atmosphere, 3b (53.8 mg, 0.2 mmol) and sodium perborate tetrahydrate

(92.3 mg, 0.6 mmol) were successively added to a 10-mL glass tube containing a magnetic

stirring bar, and the mixture was dissolved in a solution of THF (1 mL) and H2O (1 mL). The

reaction mixture was stirred vigorously at room temperature for 3 h. The volatiles were

removed under reduced pressure. Next, THF (2 mL), di-tert-butyl dicarbonate (87.3 mg, 0.4

mmol) and 4-(N,N’-dimethylamino)pyridine (2.4 mg, 0.02 mmol) were added successively to

the tube. The reaction mixture was stirred for 1 h at room temperature. Solvent was removed

under reduced pressure. The residue was then purified by silica gel chromatography (1:9

EtOAc/hexane) to give 6e (47.6 mg, 0.18 mmol in 92% isolated yield).

Procedure for the One-Carbon Homologation of 3b and the Following Oxidation

30

(Scheme 2, lower right). Under an Ar atmosphere, 3b (54.1 mg, 0.2 mmol),

bromochloromethane (51.8 mg, 0.4 mmol), and anhydrous THF (2 mL) were placed in a

10-mL glass tube containing a magnetic stirring bar. The tube was sealed with a screw cap

having a Teflon-coated silicone rubber septum. After cooling to –78 ˚C, nBuLi in hexane

(1.64 M, 207 µL, 0.34 mmol) was added to the mixture. The reaction mixture was stirred at

–78 ˚C for 5 min, and allowed to stir at room temperature for 1 h. Solvent was removed under

reduced pressure. An internal standard (1,1,2,2-tetrachloroethane) was added to the residue to

determined the yield of the product

2-methyl-8-((4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)methyl)quinoline by 1H NMR

(68%). Next, the crude material and sodium perborate tetrahydrate (138 mg, 0.9 mmol) were

placed in a 10-mL glass tube containing a magnetic stirring bar, and the mixture was

dissolved in a solution of THF (1.5 mL) and H2O (1.5 mL) under air. The reaction mixture

was stirred vigorously at room temperature for 3 h. Solvent was removed under reduced

pressure. The residue was then purified by silica gel chromatography (3:7 EtOAc/hexane) to

give 7 (21.4 mg, 0.12 mmol in 61% isolated yield based on 3b).

Procedure for the Rh-Catalyzed Heck-Type Reaction of 3b (Scheme 2, lower left). Under

an Ar atmosphere, 3b (26.9 mg, 0.1 mmol), butyl acrylate (51.7 mg, 0.4 mmol), and

[Rh(OH)(cod)]2 (1.1 mg, 0.0025 mmol) were placed in a 10-mL vial containing a magnetic

stirring bar, and the mixture was dissolved in a solution of dioxane (1 mL) and H2O (0.1 mL).

The reaction mixture was stirred at 90 ºC for 16 h. Solvent was removed under reduced

pressure. The residue was then purified by silica gel chromatography (1:9 EtOAc/hexane) to

give 8 (24.8 mg, 0.09 mmol in 92% isolated yield).

Procedure for the Pd-Catalyzed Suzuki-Miyaura Coupling of 3b (Scheme 2, upper left).

Under an Ar atmosphere, 3b (80.7 mg, 0.3 mmol), methyl 4-bromobenzoate (96.8 mg, 0.45

mmol), Pd(PPh3)4 (17.3 mg, 0.015 mmol), and K3PO4 (191 mg, 0.9 mmol) were successively

added to a 10-mL glass tube containing a magnetic stirring bar, and the mixture was

dissolved in a solution of THF (3 mL) and H2O (0.6 mL). The reaction mixture was stirred at

60 ºC for 12 h. After addition of water, the mixture was extracted with Et2O. The organic

layer was washed with brine, dried over MgSO4, filtered and concentrated. The residue was

then purified by silica gel chromatography (1:19 EtOAc/hexane) to give 9b (78.9 mg, 0.28

mmol in 94% isolated yield).

Procedure for the Ir-Catalyzed Borylation of 12 and the Following Pd-Catalyzed

31

Suzuki-Miyaura Coupling (Scheme 3). In a glove box, Silica-SMAP (0.070 mmol/g, 85.7

mg, 0.006 mmol, 2 mol%), bis(pinacolato)diboron (2) (83.8 mg, 0.33 mmol), and anhydrous,

degassed MTBE (0.5 mL) were placed in a 10-mL glass tube containing a magnetic stirring

bar. A solution of [Ir(OMe)(cod)]2 (2.0 mg, 0.003 mmol, 1 mol%) in MTBE (1 mL), and 12

(82.4 mg, 0.3 mmol) were added successively. The tube was sealed with a screw cap and

removed from the glove box. The reaction mixture was stirred at 60 ºC for 12 h, and filtered

through a glass pipette equipped with a cotton plug. Solvent was removed under reduced

pressure. An internal standard (1,1,2,2-tetrachloroethane) was added to the residue to

determine the yield of the C-8-borylated product 13 by 1H NMR (84%). Next, the crude

product (13), methyl 4-bromobenzoate (96.8 mg, 0.45 mmol), Pd(PPh3)4 (17.3 mg, 0.015

mmol), and K3PO4 (191 mg, 0.9 mmol) were placed in a 10-mL glass tube containing a

magnetic stirring bar under an Ar atmosphere, and the mixture was dissolved in a solution of

THF (3 mL) and H2O (0.6 mL). The reaction mixture was stirred at 60 ºC for 10 h. Solvent

was removed under reduced pressure. The residue was then purified by silica gel

chromatography (99:1 hexane/Et3N) to give 14 with trace amounts of impurities (68.7 mg,

0.18 mmol in 57% isolated yield based on 12). Further purification was carried out by

recrystallization from hexane to obtain the analytically pure compound.

4.3. Compound Characterization

The substrates for borylation 1a, 1b, 1f–1k, 1n and 1q were obtained from commercial

suppliers. The substrates 1c,31 1o29 and 1129 were prepared according the literature. The

substrate 1m32 was prepared via the Pd-catalyzed Suzuki-Miyaura coupling of

6-bromoquinaldine and phenylboronic acid.

2-(5-Bromopentyl)quinoline (15). Under an Ar atmosphere, nBuLi (1.64 M in hexane, 29

mL, 47 mmol) was added dropwise to a solution of quinaldine (5.73 g, 40 mmol) in THF

(200 mL) at –78 ºC. The reaction mixture was allowed to stir at 0 ºC for 1 h. The resulting

solution was added dropwise to a solution of 1,4-dibromobutane (48.2 g, 200 mmol) in THF

(200 mL) at –78 ºC via a cannula. The reaction mixture was allowed to stir at room

temperature for 12 h. After quenching with aqueous NH4Cl, the crude mixture was extracted

with EtOAc. The organic layer was washed with brine, dried over MgSO4, filtered, and

concentrated. The residue was purified by silica gel chromatography to give 15. (10.3 g, 37.2

mmol in 93% yield).

32

15N

Br5

Pale yellow oil. 1H NMR (CDCl3) δ 1.57 (quin, J = 7.5 Hz, 2H), 1.81–1.98 (m, 4H), 2.99

(t, J = 7.8 Hz, 2H), 3.42 (t, J = 6.9 Hz, 2H), 7.30 (d, J = 8.4 Hz, 1H), 7.49 (dd, J = 8.2, 7.6 Hz,

1H), 7.69 (dd, J = 8.4, 7.6 Hz, 1H), 7.79 (d, J = 8.2 Hz, 1H), 8.04 (d, J = 8.4 Hz, 1H), 8.08 (d,

J = 8.4 Hz, 1H). 13C NMR (CDCl3) δ 27.78, 28.79, 32.40, 33.53, 38.81, 121.24, 125.66,

126.65, 127.45, 128.76, 129.33, 136.22, 147.89, 162.43. HRMS–ESI (m/z): [M+H]+ Calcd

for C14H17N79Br, 278.05389; found, 278.05399.

2-(5-Methoxypentyl)quinoline (1d). A solution of 2-(5-bromopentyl)quinoline (15, 1.39 g, 5

mmol) and KOtBu (1.32 g, 10 mmol) in MeOH (10 mL) were refluxed for 21 h under an Ar

atmosphere. After quenching with aqueous NH4Cl, the crude mixture was extracted with

Et2O. The organic layer was washed with brine, dried over MgSO4, filtered and concentrated.

The residue was purified by Kugelrohr distillation to give 1d (720 mg, 3.15 mmol in 63%

yield).

1d

NOMe

5

Pale yellow oil. 1H NMR (CDCl3) δ 1.45–1.53 (m, 2H), 1.60–1.69 (m, 2H), 1.85 (quin, J

= 7.8 Hz, 2H), 2.99 (t, J = 7.8 Hz, 2H), 3.33 (s, 3H), 3.38 (t, J = 6.6 Hz, 2H), 7.31 (d, J = 8.2

Hz, 1H), 7.49 (ddd, J = 8.2, 7.6, 1.5 Hz, 1H), 7.69 (ddd, J = 8.2, 7.6, 1.5 Hz, 1H), 7.78 (dd, J

= 8.2, 1.5 Hz, 1H), 8.04 (d, J = 8.2 Hz, 1H), 8.08 (d, J = 8.2 Hz, 1H). 13C NMR (CDCl3) δ

25.85, 29.27, 29.57, 39.03, 58.29, 72.51, 121.25, 125.54, 126.62, 127.39, 128.75, 129.21,

136.10, 147.89, 162.77. HRMS–ESI (m/z): [M+H]+ Calcd for C15H20NO, 230.15394; found,

230.15424.

N,N-Diethyl-5-(quinolin-2-yl)pentan-1-amine (1e). A mixture of

2-(5-bromopentyl)quinoline (15, 1.39 g, 5 mmol) and diethylamine (10 mL) were refluxed

for 22 h under an Ar atmosphere. After quenching with aqueous NH4Cl, the crude mixture

was extracted with Et2O. The organic layer was washed with brine, dried over MgSO4,

filtered and concentrated. The residue was purified by Kugelrohr distillation to give 1e (1.22

g, 4.5 mmol in 90% yield).

33

1e

NNEt25

Pale yellow oil. 1H NMR (CDCl3) δ 1.01 (t, J = 7.2 Hz, 6H), 1.38–1.55 (m, 4H), 1.84

(quin, J = 7.8 Hz, 2H), 2.41 (t, J = 7.5 Hz, 2H), 2.51 (q, J = 7.2 Hz, 4H), 2.98 (t, J = 7.8 Hz,

2H), 7.31 (d, J = 8.4 Hz, 1H), 7.49 (dd, J = 8.5, 7.5 Hz, 1H), 7.69 (dd, J = 8.4, 7.5 Hz, 1H),

7.79 (d, J = 8.5 Hz, 1H), 8.04 (d, J = 8.4 Hz, 1H), 8.08 (d, J = 8.4 Hz, 1H). 13C NMR

(CDCl3) δ 11.37 (2C), 26.63, 27.32, 29.70, 39.04, 46.57 (2C), 52.61, 121.16, 125.44, 126.53,

127.30, 128.70, 129.11, 135.98, 147.83, 162.78. HRMS–ESI (m/z): [M+H]+ Calcd for

C18H27N2, 271.21688; found, 271.21716.

tert-Butyl (2-Methylquinolin-6-yl) Carbonate (1l). The title compound (1l) was prepared

through the Boc-protection of 6-hydroxy-2-methylquinoline.33

1l

N Me

BocO

White solid. M.p. 89–91 ˚C. 1H NMR (CDCl3) δ 1.59 (s, 9H), 2.74 (s, 3H), 7.30 (d, J =

8.5 Hz, 1H), 7.51 (dd, J = 8.5, 2.7 Hz, 1H), 7.60 (d, J = 2.7 Hz, 1H), 8.02 (d, J = 8.5 Hz, 1H),

8.02 (d, J = 8.5 Hz, 1H). 13C NMR (CDCl3) δ 25.14, 27.56 (3C), 83.82, 117.77, 122.54,

124.26, 126.62, 130.15, 135.92, 145.88, 148.31, 151.90, 158.95. HRMS–ESI (m/z): [M+H]+

Calcd for C15H18NO3, 260.12812; found, 260.12833.

2,5,7-Trimethylquinoline (1p).34 The title compound (1p) was prepared through the

Doebner-Miller reaction of 3,5-dimethylaniline and crotonaldehyde.35

1p

N MeMe

Me

Colorless liquid. 1H NMR (CDCl3) δ 2.47 (s, 3H), 2.56 (s, 3H), 2.69 (s, 3H), 7.09 (s, 1H),

7.16 (d, J = 8.7 Hz, 1H), 7.65 (s, 1H), 8.06 (d, J = 8.7 Hz, 1H). 13C NMR (CDCl3) δ 18.14,

21.52, 24.91, 120.56, 123.68, 125.88, 128.37, 132.23, 133.79, 139.97, 148.38, 158.25.

7-Methoxy-2-methyl-N,N-dipropylquinolin-4-amine (12). 11 (831 mg, 4 mmol),

p-toluenesulfonic acid monohydrate (1.3 g, 7.5 mmol), and dipropylamine (5 mL) were

placed in a 50-mL glass tube containing a magnetic stirring bar. The reaction mixture was

stirred at 160 ºC for 16 h, and then cooled to room temperature. After addition of water, the

34

mixture was extracted with CH2Cl2. The organic layer was washed with brine, dried over

MgSO4, filtered and concentrated. The residue was purified by silica gel chromatography

(50:49:1 EtOAc/hexane/Et3N) followed by Kugelrohr distillation to give 12 (895 mg, 3.28

mmol in 82% yield).

N Me

N

MeO

12 Pale yellow viscous liquid. 1H NMR (CDCl3) δ 0.87 (t, J = 7.5 Hz, 6H), 1.59 (sext, J = 7.5

Hz, 4H), 2.62 (s, 3H), 3.23 (t, J = 7.5 Hz, 4H), 3.92 (s, 3H), 6.63 (s, 1H), 7.03 (dd, J = 9.0,

2.7 Hz, 1H), 7.30 (d, J = 2.7 Hz, 1H), 7.90 (d, J = 9.0 Hz, 1H). 13C NMR (CDCl3) δ 11.40

(2C), 20.05 (2C), 25.42, 54.48 (2C), 55.28, 107.33, 109.32, 116.44, 117.67, 125.28, 151.59,

156.53, 159.20, 160.31. HRMS–ESI (m/z): [M+H]+ Calcd for C17H25N2O, 273.19614; found,

273.19617.

8-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)quinaldine (3b)36

3b

N Me

Bpin 1H NMR (CDCl3) δ 1.48 (s, 12H), 2.71 (s, 3H), 7.23 (d, J = 8.4 Hz, 1H), 7.44 (dd, J = 7.9,

6.9 Hz, 1H), 7.77 (dd, J = 7.9, 1.5 Hz, 1H), 7.89 (dd, J = 6.9, 1.5 Hz, 1H), 7.97 (d, J = 8.4 Hz,

1H). 13C NMR (CDCl3) δ 24.76 (4C), 25.46, 83.98 (2C), 121.61, 125.02, 125.77, 129.20,

134.63, 135.91, 151.30, 158.93. A signal for the carbon directly attached to the boron atom

was not observed. 11B NMR (CDCl3) δ 32.01.

2-Propyl-8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinoline (3c)

3c

N nPr

Bpin

Pale yellow oil. 1H NMR (CDCl3) δ 1.02 (t, J = 7.5 Hz, 3H), 1.47 (s, 12H), 1.92 (sext, J =

7.5 Hz, 2H), 2.95 (t, J = 7.5 Hz, 2H), 7.22 (d, J = 8.4 Hz, 1H), 7.44 (dd, J = 8.1, 6.9 Hz, 1H),

7.78 (dd, J = 8.1, 1.5 Hz, 1H), 7.88 (dd, J = 6.9, 1.5 Hz, 1H), 7.98 (d, J = 8.4 Hz, 1H). 13C

NMR (CDCl3) δ 13.92, 21.62, 24.79 (4C), 40.77, 83.90 (2C), 121.29, 125.00, 126.02, 129.23,


was not observed. 11B NMR (CDCl3) δ 32.18. HRMS–APCI (m/z): [M+H]+ Calcd for

C18H2510BNO2, 297.20092; found, 297.20126.

35

2-(5-Methoxypentyl)-8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinoline (3d)

3d

N

Bpin

OMe5

Colorless oil. 1H NMR (CDCl3) δ 1.42–1.52 (m, 14H), 1.66 (quin, J = 6.6 Hz, 2H), 1.94

(quin, J = 7.8 Hz, 2H), 2.98 (t, J = 7.8 Hz, 2H), 3.33 (s, 3H), 3.39 (t, J = 6.6 Hz, 2H), 7.22 (d,

J = 8.4 Hz, 1H), 7.44 (dd, J = 7.8, 6.9 Hz, 1H), 7.78 (d, J = 7.8 Hz, 1H), 7.89 (d, J = 6.9 Hz,

1H), 7.98 (d, J = 8.4 Hz, 1H). 13C NMR (CDCl3) δ 24.77 (4C), 25.80, 28.19, 29.47, 38.65,

58.42, 72.76, 83.84 (2C), 121.20, 124.98, 125.99, 129.24, 134.64, 135.80, 151.19, 162.17. A

signal for the carbon directly attached to the boron atom was not observed. 11B NMR

(CDCl3) δ 32.13. HRMS–APCI (m/z): [M+H]+ Calcd for C21H3110BNO3, 355.24278; found,

355.24330.

2-(5-(N,N-Diethylamino)pentyl)-8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinolin

e (3e)

3e

N

Bpin

NEt25

Pale yellow solid. M.p. 123–129 ˚C. 1H NMR (CDCl3) δ 1.20 (br-s, 6H), 1.39–1.60 (m,

14H), 1.68 (br-s, 2H), 1.96 (quin, J = 7.8 Hz, 2H), 2.80 (br-s, 6H), 2.98 (t, J = 7.8 Hz, 2H),

7.22 (d, J = 8.5 Hz, 1H), 7.45 (dd, J = 8.1, 6.9 Hz, 1H), 7.79 (dd, J = 8.1, 1.5 Hz, 1H), 7.89

(dd, J = 6.9, 1.5 Hz, 1H), 7.99 (d, J = 8.5 Hz, 1H). 13C NMR (CDCl3) δ 9.51, 24.64 (4C),

26.66, 27.69, 38.31, 46.24, 51.60, 83.70 (2C), 121.09, 124.93, 125.84, 129.11, 134.47, 135.82,

150.96, 161.68. A signal for the carbon directly attached to the boron atom was not observed. 11B NMR (CDCl3) δ 32.21. HRMS–EI (m/z): [M]+ Calcd for C24H37

11BO2N2, 396.2948;

found, 396.2954.

4-Chloro-8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinaldine (3i)

3i

N Me

Bpin

Cl

White solid. M.p. 78–87 ˚C. 1H NMR (CDCl3) δ 1.48 (s, 12H), 2.69 (s, 3H), 7.35 (s, 1H),

7.54 (dd, J = 8.4, 6.9 Hz, 1H), 7.92 (dd, J = 6.9, 1.5 Hz, 1H), 8.19 (dd, J = 8.4, 1.5 Hz, 1H). 13C NMR (CDCl3) δ 24.71 (4C), 25.17, 84.15 (2C), 121.56, 124.04, 125.43, 126.06, 135.42,

36

142.11, 151.94, 158.76. A signal for the carbon directly attached to the boron atom was not

observed. 11B NMR (CDCl3) δ 31.91. HRMS–APCI (m/z): [M+H]+ Calcd for

C16H2010BClNO2, 303.13065; found, 303.13104.

2,6-Dimethyl-8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinoline (3j)

3j

N Me

Bpin

Me

Pale yellow solid. M.p. 122–129 ˚C. 1H NMR (CDCl3) δ 1.48 (s, 12H), 2.49 (s, 3H), 2.69

(s, 3H), 7.19 (d, J = 8.4 Hz, 1H), 7.53 (br-s, 1H), 7.73 (br-s, 1H), 7.89 (d, J = 8.4 Hz, 1H). 13C NMR (CDCl3) δ 21.16, 24.76 (4C), 25.39, 83.94 (2C), 121.56, 125.88, 128.27, 134.48,



C17H2310BNO2, 283.18527; found, 283.18537.

6-Chloro-8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinaldine (3k)

3k

N Me

Bpin

Cl

White solid. M.p. 148–157 ˚C. 1H NMR (CDCl3) δ 1.48 (s, 12H), 2.70 (s, 3H), 7.25 (d, J

= 8.4 Hz, 1H), 7.75 (d, J = 2.4 Hz, 1H), 7.80 (d, J = 2.4 Hz, 1H), 7.90 (d, J = 8.4 Hz, 1H). 13C NMR (CDCl3) δ 24.73 (4C), 25.40, 84.36 (2C), 122.49, 126.59, 127.69. 130.87, 135.04,

149.56, 159.32. A signal for the carbon directly attached to the boron atom was not observed. 11B NMR (CDCl3) δ 31.58. HRMS–APCI (m/z): [M+H]+ Calcd for C16H20

10BClNO2,

303.13065; found, 303.13091.

6-Phenyl-8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinaldine (3m)

3m

N Me

Bpin

Ph


= 8.4 Hz, 1H), 7.34–7.39 (m, 1H), 7.45–7.50 (m, 2H), 7.73 (d, J = 7.5 Hz, 2H), 7.96 (d, J =

2.1 Hz, 1H), 8.03 (d, J = 8.4 Hz, 1H), 8.14 (d, J = 2.1 Hz, 1H). 13C NMR (CDCl3) δ 24.79

(4C), 25.50, 84.09 (2C), 122.01, 125.99, 127.04, 127.38, 127.49 (2C), 128.81 (2C), 134.35,

136.14, 137.69, 140.75, 150.74, 158.99. A signal for the carbon directly attached to the boron

37

atom was not observed. 11B NMR (CDCl3) δ 32.41. HRMS–EI (m/z): [M]+ Calcd for

C22H2411BNO2, 345.1900; found, 345.1895.

7-Chloro-8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinaldine (3n)

3n

N Me

Bpin

Cl


= 8.4 Hz, 1H), 7.38 (d, J = 8.4 Hz, 1H), 7.66 (d, J = 8.4 Hz, 1H), 7.94 (d, J = 8.4 Hz, 1H). 13C NMR (CDCl3) δ 24.64 (4C), 25.14, 84.63 (3C), 121.86, 123.93, 126.49, 129.31, 135.51,

137.88, 151.77, 159.72. A signal for the carbon directly attached to the boron atom was not

observed. 11B NMR (CDCl3) δ 31.54. HRMS–APCI (m/z): [M+H]+ Calcd for

C16H2010BClNO2, 303.13065; found, 303.13080.

7-Methoxy-8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinaldine (3o)

3o

N Me

Bpin

MeO

White solid. M.p. 115–123 ºC. 1H NMR (CDCl3) δ 1.50 (s, 12H), 2.64 (s, 3H), 3.93 (s,

3H), 7.06 (d, J = 8.1 Hz, 1H), 7.15 (d, J = 9.0 Hz, 1H), 7.70 (d, J = 9.0 Hz, 1H), 7.88 (d, J =

8.1 Hz, 1H). 13C NMR (CDCl3) δ 24.67 (4C), 25.22, 56.12, 84.03 (2C), 112.43, 119.53,

121.08, 129.71, 135.34, 152.49, 159.27, 162.72. A signal for the carbon directly attached to

the boron atom was not observed. 11B NMR (CDCl3) δ 32.44. HRMS–EI (m/z): [M]+ Calcd

for C17H2211BO3N, 299.1693; found, 299.1682.

2,5,7-Trimethyl-8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinoline (3p)

3p

N Me

Bpin

Me

Me

White solid. M.p. 93–98 ˚C. 1H NMR (CDCl3) δ 1.50 (s, 12H), 2.50 (s, 3H), 2.58 (s, 3H),

2.64 (s, 3H), 7.08 (s, 1H), 7.14 (d, J = 8.7 Hz, 1H), 8.06 (d, J = 8.7 Hz, 1H). 13C NMR

(CDCl3) δ 18.23, 21.88, 24.74 (4C), 24.87, 83.82 (2C), 120.28, 123.00, 128.42, 131.73,



C18H2510BNO2, 297.20092; found, 297.20102.

38

2,3-Dimethyl-5,8-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinoxaline (3q)

3q

N

N

Me

Bpin

Me

Bpin

White solid. M.p. 215–227 ˚C. 1H NMR (CDCl3) δ 1.46 (s, 24H), 2.67 (s, 6H), 7.87 (s,

2H). 13C NMR (CDCl3) δ 23.38 (2C), 24.72 (8C), 84.06 (4C), 134.06 (2C), 143.83 (2C),

152.86 (2C). A signal for the carbons directly attached to the boron atoms was not observed. 11B NMR (CDCl3) δ 31.98. HRMS–EI (m/z): [M]+ Calcd for C22H32

11B2O4N2, 410.2548;

found, 410.2550.

tert-Butyl Quinolin-8-yl Carbonate (6a)37

N

OBoc 6a

White solid. 1H NMR (CDCl3) δ 1.61 (s, 9H), 7.44 (dd, J = 8.4, 4.2 Hz, 1H), 7.52–7.54 (m,

2H), 7.70–7.74 (m, 1H), 8.18 (dd, J = 8.4, 1.6 Hz, 1H), 8.94 (dd, J = 4.2, 1.6 Hz, 1H). 13C

NMR (CDCl3) δ 27.52 (3C), 83.59, 120.98, 121.77, 125.75, 126.18, 129.47, 135.90, 141.34,

147.49, 150.51, 152.13.

tert-Butyl (2-Methylquinolin-8-yl) Carbonate (6b)

N Me

OBoc 6b


8.4 Hz, 1H), 7.41–7.50 (m, 2H), 7.66 (dd, J = 7.5, 2.1 Hz, 1H), 8.05 (d, J = 8.4 Hz, 1H). 13C

NMR (CDCl3) δ 25.48, 27.55 (3C), 83.28, 120.65, 122.71, 125.23, 125.44, 127.74, 135.95,

140.72, 147.16, 152.23, 159.29. HRMS–ESI (m/z): [M+Na]+ Calcd for C15H17NO3Na,

282.11006; found, 282.11018.

tert-Butyl (3-Methylquinolin-8-yl) Carbonate (6f)38

6f

N

OBoc

Me

White solid. 1H NMR (CDCl3) δ 1.60 (s, 9H), 2.51 (s, 3H), 7.43–7.51 (m, 2H), 7.62 (dd, J

39

= 7.5, 2.2 Hz, 1H), 7.93 (br-s, 1H), 8.79 (d, J = 1.8 Hz, 1H). 13C NMR (CDCl3) δ 18.56,

27.54 (3C), 83.51, 119.94, 125.12, 126.21, 129.43, 131.33, 134.49, 139.61, 147.51, 152.21,

152.55.

tert-Butyl (4-Methylquinolin-8-yl) Carbonate (6g)

6g

N

OBoc

Me

White solid. M.p. 98–100 ˚C. 1H NMR (CDCl3) δ 1.60 (s, 9H), 2.71 (s, 3H), 7.24–7.28 (m,

1H), 7.50–7.57 (m, 2H), 7.89 (dd, J = 6.9, 2.4 Hz, 1H), 8.79 (d, J = 4.4 Hz, 1H). 13C NMR

(CDCl3) δ 18.70, 27.51 (3C), 83.46, 120.63, 121.84, 122.51, 125.76, 129.56, 141.18, 144.34,

147.93, 150.17, 152.21. HRMS–ESI (m/z): [M+H]+ Calcd for C15H18NO3, 260.12812; found,

260.12860.

tert-Butyl (6-Methoxyquinolin-8-yl) Carbonate (6h)

6h

N

OBoc

MeO


2.7 Hz, 1H), 7.23 (d, J = 2.7 Hz, 1H), 7.38 (dd, J = 8.4, 4.2 Hz, 1H), 8.05 (dd, J = 8.4, 1.5 Hz,

1H), 8.77 (dd, J = 4.2, 1.5 Hz, 1H). 13C NMR (CDCl3) δ 27.51 (3C), 55.60, 83.73, 103.29,

114.08, 122.15, 129.99, 134.69, 137.63, 147.96, 148.29, 151.87, 157.45. HRMS–ESI (m/z):

[M+Na]+ Calcd for C15H17NO4Na, 298.10498; found, 298.10552.

(2-Methylquinolin-8-yl)methanol (7)

N Me

OH 7

White solid. M.p. 70–73 ˚C. 1H NMR (CDCl3) δ 2.73 (s, 3H), 5.17 (s, 2H), 5.76 (br-s, 1H),

7.30 (d, J = 8.4 Hz, 1H), 7.40 (dd, J = 8.4, 6.6 Hz, 1H), 7.50 (d, J = 6.6 Hz, 1H), 7.69 (d, J =

8.4 Hz, 1H), 8.07 (d, J = 8.4 Hz, 1H). 13C NMR (CDCl3) δ 25.33, 65.23, 122.04, 125.52,

126.69, 127.10, 127.64, 137.02, 137.28, 146.89, 158.00. HRMS–ESI (m/z): [M+H]+ Calcd

for C11H12NO, 174.09134; found, 174.09174.

(E)-Butyl 3-(2-Methylquinolin-8-yl)acrylate (8)

40

N Me

CO2Bu

8

Red-brown oil. 1H NMR (CDCl3) δ 0.99 (t, J = 7.2 Hz, 3H), 1.44–1.54 (m, 2H), 1.69–1.79

(m, 2H), 2.78 (s, 3H), 4.26 (t, J = 6.9 Hz, 2H), 6.84 (d, J = 16.2 Hz, 1H), 7.33 (d, J = 8.1 Hz,

1H), 7.46–7.52 (m, 1H), 7.81 (dd, J = 8.1, 1.2 Hz, 1H), 7.96 (dd, J = 7.5, 1.2 Hz, 1H), 8.04 (d,

J = 8.1 Hz, 1H), 8.97 (d, J = 16.2 Hz, 1H). 13C NMR (CDCl3) δ 13.66, 19.12, 25.52, 30.73,

64.28, 120.11, 122.40, 125.33, 126.68, 127.89, 129.81, 132.38, 136.28, 141.40, 145.88,

159.33, 167.57. HRMS–ESI (m/z): [M+Na]+ Calcd for C17H19NO2Na, 292.13080; found,

292.13120.

Methyl 4-(2-Methylquinolin-8-yl)benzoate (9b)

N Me

CO2Me

9b


8.4 Hz, 1H), 7.55 (dd, J = 8.1, 7.2 Hz, 1H), 7.74 (dd, J = 7.2, 1.5 Hz, 1H), 7.81 (dd, J = 8.1,

1.5 Hz, 1H), 7.87 (d, J = 8.4 Hz, 2H), 8.09 (d, J = 8.4 Hz, 1H), 8.15 (d, J = 8.4 Hz, 2H). 13C

NMR (CDCl3) δ 25.51, 51.93, 121.99, 125.33, 126.91, 127.99, 128.59, 128.99 (2C), 130.31,

131.03 (2C), 136.27, 138.76, 144.47, 145.27, 159.08, 167.41. HRMS–ESI (m/z): [M+H]+

Calcd for C18H16NO2, 278.11756; found, 278.11798.

Methyl 4-(6-((tert-Butoxycarbonyl)oxy)-2-methylquinolin-8-yl)benzoate (9l)

9l

N Me

BocO

CO2Me White solid. M.p. 106–112 ˚C. 1H NMR (CDCl3) δ 1.60 (s, 9H), 2.67 (s, 3H), 3.96 (s, 3H),

7.32 (d, J = 8.4 Hz, 1H), 7.57 (d, J = 2.7 Hz, 1H), 7.62 (d, J = 2.7 Hz, 1H), 7.85 (d, J = 8.4

Hz, 2H), 8.05 (d, J = 8.4 Hz, 1H), 8.15 (d, J = 8.4 Hz, 2H). 13C NMR (CDCl3) δ 25.39, 27.54

(3C), 51.96, 83.90, 118.04, 122.53, 124.81, 127.27, 128.96, 129.03 (2C), 131.02 (2C), 136.09,

140.42, 143.30, 143.40, 147.74, 151.88, 158.90, 167.28. HRMS–ESI (m/z): [M+Na]+ Calcd

for C23H23NO5Na, 416.14684; found, 416.14771.

41

8-(4-Chlorophenyl)-7-methoxy-2-methyl-N,N-dipropylquinolin-4-amine (14)

N Me

N

MeO

Cl

14

White solid. M.p. 95–98 ˚C. 1H NMR (CDCl3) δ 0.90 (t, J = 7.5 Hz, 6H), 1.61 (sext, J =

7.5 Hz, 4H), 2.51 (s, 3H), 3.23 (t, J = 7.5 Hz, 4H), 3.88 (s, 3H), 6.65 (s, 1H), 7.26 (d, J = 9.3

Hz, 1H), 7.40–7.48 (m, 4H), 8.08 (d, J = 9.3 Hz, 1H). 13C NMR (CDCl3) δ 11.51 (2C), 20.04

(2C), 25.98, 54.68 (2C), 56.36, 109.62, 110.92, 118.55, 124.70, 124.99, 127.45 (2C), 132.23,

133.52 (2C), 134.34, 148.82, 156.24, 156.31, 159.43. HRMS–ESI (m/z): [M+H]+ Calcd for

C23H28N2OCl, 383.18847; found, 383.18888.

4.4. X-ray Crystallographic Analysis

Single crystal of 3n was obtained by recrystallization from hexane. Data of 3n were

collected on a Rigaku AFC-7R diffractometer with a mercury CCD area detector, graphite

monochromated Mo-Kα radiation (λ = 0.71069 Å) at 150 K, and processed using

CrystalClear (Rigaku).39 The structure was solved by a direct method (SIR2004)40 and

refined by full-matrix least-square refinement on F2. The non-hydrogen atoms were refined

anisotropically. The hydrogen atoms were located on the calculated positions and refined

using a riding model. All calculations were performed using the CrystalStructure software

package.41 CCDC 943646 contains the supplementary crystallographic data for this paper.

These data can be obtained free of charge from the Cambridge Crystallographic Data Centre

via www.ccdc.cam.ac.uk/data_request/cif.

Crystal data for 3n: C16H19BClNO2, M = 303.59, orthorhombic, space group = Pbca (#61),

a = 8.1914(11) Å, b = 12.942(2) Å, c = 29.341(4) Å, V = 3110.4(8) Å3, Z = 8, density (calc.)

= 1.297 g/cm3, total reflections collected = 23343, unique reflections = 3685 (Rint = 0.0538),

GOF = 1.108. The final R1 factor was 0.0504 (I>2σ(I)) (wR2 = 0.1325, all data).

5. References

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42

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G.; Kawamorita, S.; Ochida, A.; Akiyama, R.; Hara, K.; Fukuoka, A.; Asakura, K.;

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(16) For the Ir-catalyzed C–H borylation of arenes based on the directing effect of a

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López-Rodríguez, R.; Álvarez, E.; Fernández, R.; Lassaletta, J. M. Angew. Chem. Int.

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Fernández, R.; Lassaletta, J. M. J. Am. Chem. Soc. 2012, 134, 4573–4576. For the

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Clark, T. B. Org. Lett. 2012, 14, 3558–3561.

(17) 1,2-Dihydroquinoline was not detected in the crude product. No trace of 2-borylation

was observed.

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Zhang, Y.; Li, M.; Chandrasekaran, S.; Gao, X.; Fang, X.; Lee, H.-W.; Hardcastle, K.;

Yang, J.; Wang, B. Tetrahedron 2007, 63, 3287–3292. See also ref. 13.

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Arrowsmith, M.; Hill, M. S.; Hadlington, T.; Kociok-Köhn, G.; Weetman, C.

Organometallics 2011, 30, 5556–5559. (b) Oshima, K.; Ohmura, T.; Suginome, M. J.

Am. Chem. Soc. 2012, 134, 3699–3702.

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44



(c) Ochida, A.; Hamasaka, G.; Yamauchi, Y.; Kawamorita, S.; Oshima, N.; Hara, K.;

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corresponding O-tert-butoxycarbonyl-8-hydroxyquinoline 6 through the

oxidation/Boc-protection protocol.

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T.; Lynch, V. M.; Furuta, H. J. Am. Chem. Soc. 2002, 24, 13474–13479. (b) Myers, M.

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45

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46

Chapter 2

Synthesis, Coordination Property and Reactivity of Silica-Supported Triptycene-type Phosphine

A silica-supported triptycene-type phosphine, Silica-TRIP, comprising a

9-phospha-10-silatriptycene (TRIP) and silica gel as a P-coordination center and a solid

support, respectively, was synthesized and structurally characterized by nitrogen absorption

measurements and solid-state CP/MAS NMR spectroscopy. Silica-TRIP exhibited a

mono-P-ligating feature toward a Pd(II) complex, resulting in selective formation of a 1:1

Pd-P species even with an excess amount of the ligand. As a result, Silica-TRIP enabled

Pd-catalyzed Suzuki–Miyaura cross-coupling reactions of chloroarenes under mild conditions,

regardless of the moderate electron-donating nature of the triarylphosphine-based ligand.

47

1. Introduction

Silica-supported ligands,1 which are generally synthesized by silane coupling between

silicon-functionalized organic molecules and a silanol-containing surface, have been widely

studied to prepare heterogenized transition metal catalysts with practical merits such as easy

separation and reusability.2,3 However, steric hindrance of the solid surface toward the active

site often causes a decrease in catalytic performance compared to the corresponding

homogeneous molecular catalysts. Moreover, commonly used flexible linkers (e.g., alkyl

chains) between ligands and silica gel impart significant mobility to the coordination centers,

resulting in difficulty in ligand design based on the features of the solid surface.

Recently, Sawamura et al. have designed and synthesized a silica-supported

monophosphine, Silica-SMAP (Figure 1a), providing a novel example of increased catalytic

activity by surface immobilization.4 The rigidity of the caged trialkylphosphine (SMAP)5 and

the cage-to-surface immobilization made the P-coordination center stand upward on the

surface and hence exist in isolation (Figure 1b). Thus, Silica-SMAP could form 1:1

metal-phosphine complexes exclusively with a range of transition metal species regardless of

its compactness.

(a) (b)

Si

P

OSiOO

O

Silica-SMAP

OSiOO

O

SiMe3

SiO2

Si

P

OSiOO

OSiO2

Si

P

Figure 1. (a) Structure of Silica-SMAP and (b) restricted mobility of the SMAP moiety on

silica surface.

The transition metal complexes prepared in this manner performed as useful

heterogeneous catalysts for various reactions. On the basis of these considerations,

9-phospha-10-silatriptycenes (TRIP)6 was noticed as a new motif for silica-supported ligands.

Silica-supported triptycene-type phosphine Silica-TRIP (Figure 2) was expected to function

as a supported ligand complementary to Silica-SMAP-based systems. SMAP and TRIP

moieties are trialkyl- and triarylphosphines, respectively, thus having contrasting electronic

natures; the former should be much more electron-donating. The two ligands also differ in

steric demand; the latter is significantly bulkier.

48

SiO2

OSiOO

O

P

SiOSiOO

O

SiMe3

Silica-TRIP Figure 2. Structure of Silica-TRIP.

In fact, a Silica-TRIP-Rh catalyst system realized heteroatom-directed borylation of

C(sp3)–H bonds of amides, ureas, and 2-aminopyridines at the position α to the N atom, for

which Silica-SMAP was not effective, affording the corresponding primary and secondary

α-aminoalkylboronates (Scheme 1, top).7 On the other hand, both Silica-TRIP and

Silica-SMAP were effective for the Ir-catalyzed N-directed C(sp3)–H borylation of

2-alkylpyridines (Scheme 1, middle).4j

Scheme 1. Transformations of C(sp3)–H and C(sp2)–Cl bonds with Silica-TRIP-metal

catalyst systems.

Cl (HO)2B

cat.[Silica-TRIP-Pd]

base+

Y N

X

R2R1

H

+ pinB–Bpin

cat.[Silica-TRIP-Rh]

Y N

X

R2R1

Bpin

R4 R5 R4 R5

N-Adjacent C–H transformation (Ref. 7)

C–Cl transformation (This work)

N

R3

H

+ pinB–Bpin

[Silica-SMAP-Ir]or

[Silica-TRIP-Ir]N

R3

Bpin

C–H transformation (Ref. 4j)cat.

This chapter describes details of those studies on the synthesis of Silica-TRIP,4h its

coordination properties toward Pd(II) complexes, and its catalytic application to Pd-catalyzed

Suzuki–Miyaura cross-coupling of chloroarenes (Scheme 1, bottom).8,9 The use of bulky and

electron-rich monophosphine10 or NHC11 ligands is a common strategy for enabling the

Pd-catalyzed cross-coupling of chloroarenes under mild conditions, and there are only a

limited number of reports on effective catalyst systems with moderately electron-donating

49

triarylphosphine-based ligands; chloroarenes are more desirable but less reactive than

bromoarenes and iodoarenes.12–15


The precursor for Silica-TRIP, a soluble triptycene-type phosphine 3 having a silanol

group at the bridgehead, was synthesized following to Tsuji and Tamao’s procedure for the

synthesis of 9-phospha-10-silatriptycenes with a slight modification.6 Thus, commercially

available 1-bromo-2-iodobenzene (1) was converted to tris(o-bromophenyl)phosphine (2) by

treatment with iPrMgBr for Mg-I exchange at –20 °C,16 followed by the reaction with PCl3 in

the presence of N,N,N',N'-tetramethylethylenediamine (TMEDA) as an additive. This

procedure avoids the extremely low temperature conditions (–110 °C) employed in Tsuji and

Tamao’s procedure.6 The trilithiated species generated from 2 with 6 equivalents of tBuLi in

Et2O/THF was reacted with SiCl4. Purification by silica gel chromatography gave the silanol

HO-TRIP (3) in 70% yield as an air- and moisture-stable solid.

Scheme 2. Preparation of silanol HO-TRIP (3).

I

Br

1) iPrMgBr (3.5 equiv) THF, –20 ºC, 3 h

1(3.5 equiv)

2) PCl3 (1 equiv) TMEDA (3.5 equiv) THF, –20 °C then 0 °C, 14 h

P

Br2 57%

3

1) tBuLi (6 equiv) Et2O/THF (5:1) –78 ºC, 4 h

2) SiCl4 (1 equiv) Et2O/THF (5:1) –78 °C, 4 h3) workup with SiO2

OH

P

Si

HO-TRIP (3)70%

Single-crystal X-ray diffraction analysis of 3 confirmed its three-dimensional molecular

structure having a triptycene cage, the bridgehead of which was substituted with P and Si

atoms (Figure 3).

50

Figure 3. Molecular structure of 3 at 50% probability level; a solvent molecule (CHCl3) and

one of the disordered hydrogen atoms of the silanol moiety (SiO–H) are omitted for clarity.

Interestingly, six molecules of 3 in the crystal structure adopted a chair form

hydrogen-bonding network consisting of six silanol groups as shown in Figure 4 (average

distance of Ar3SiO···OSiAr3; 2.651 Å).17 The existence of the silanol group was supported by

the observation of a broad absorption band at 3347 cm–1 by IR spectroscopy, which was

assignable to an (Si)O–H stretching vibration.

Figure 4. Chair form hydrogen-bonding network (blue-dotted lines) of 3 in the crystal

structure.

51

The triarylsilanol 3 did not react with silica gel during the chromatography, while the

purified 3 underwent slow self-condensation to form the corresponding disiloxane (TRIP)2O

(4). The self-condensation was more rapid in the presence of a base. In fact, heating of 3 with

imidazole in benzene at 80 °C caused its complete consumption, forming white precipitates

(Scheme 3).18 Filtration of the precipitates gave the disiloxane 4 in 52% isolated yield.

Treatment of the silanol 3 with N-trimethylsilylimidazole provided the

1,1,1-trimethyl-substituted disiloxane TMSO-TRIP (5) in 87% yield (Scheme 4).

Scheme 3. Preparation of disiloxane (TRIP)2O (4).

3(2 equiv)

imidazole(0.4 equiv)

benzene80 °C, 10.5 h

(TRIP)2O (4) 52%

O

P

Si

Si

P

Scheme 4. Preparation of disiloxane TMSO-TRIP (5).

3

Me3Si-imidazole(5 equiv)

CH2Cl2, rt, 1 h O

P

Si

Me3SiTMSO-TRIP (5) 87%

The preparation of silica-supported triptycene-type phosphine (Silica-TRIP) with a direct

disiloxane linkage is shown in Scheme 5. Slight modifications were made to the procedure

described in the initial report4h for more expeditious operation in large-scale synthesis.

Specifically, the silanol phosphine 3 was grafted to a silica gel surface (CARiACT Q10,

75–150 µm) in the presence of imidazole and toluene under gentle stirring at 100 °C over 16

h. The resulting colorless solids were collected by filtration, washed successively with

degassed toluene, toluene-MeOH (1:1), and MeOH, and then dried under vacuum to afford

phosphine-functionalized silica-gel Silica-TRIP(SiOH). Unreacted surface silanols were

Me3Si-endcapped through treatment with excess N-trimethylsilylimidazole in THF at 60 °C

for 24 h, to furnish Silica-TRIP. The P loading to silica gel was calculated to be 0.078

mmol/g based on the ability of the gel to bind a Pd(II) complex in a 1:1 Pd/P coordination

mode (vide infra).

52

Scheme 5. Preparation of Silica-TRIP.

Me3Si-imidazole

THF60 °C24 h

silica gelimidazole

toluene100 °C16 h

SiO2

OSiO

OO

P

SiOSiO

OO

SiMe3

Silica-TRIPSiO2

OSiO

OO

P

SiOHSiOO

O

Silica-TRIP(SiOH)

3

Figure 5 shows nitrogen adsorption-desorption isotherms and Barrett-Joyner-Halenda

(BJH) plots for Silica-TRIP. The structural parameters (specific surface area, pore diameter

and pore volume) are summarized in Table 1. Silica-TRIP exhibited a hysteresis loop,

indicating the existence of mesopores with a broad pore-diameter distribution at an average

of 17.2 nm. The surface modification of CARiACT Q10 silica gel (75–150 µm) for the

preparation of Silica-TRIP as well as Silica-SMAP reasonably reduced their structural

parameters such as surface area and pore volume.4c A surface P density of Silica-TRIP on the

basis of the surface area (244 m2/g) and the estimated TRIP loading (0.078 mmol/g) was

calculated to be 0.19 nm–2. This value was comparable to that of Silica-SMAP (0.19 nm–2).

53

(a)

(b)

Figure 5. (a) Nitrogen adsorption–desorption isotherms and (b) BJH pore-diameter

distribution plots of Silica-TRIP.

54

Table 1. Structural parameters.

materials surface area (BET, m2/g)

pore diameter (nm)

pore volume (mL/g)

Silica-TRIP 244 17.2 1.05

Silica-SMAPa 220 17.3 1.08

CARiACT Q10a 284 17.8 1.32 a Data were taken from ref 4c.

The silica-supported phosphine Silica-TRIP was characterized by solid-state 31P, 13C,

and 29Si NMR spectroscopies with comparison to the solution NMR spectra of the soluble

disiloxane phosphine 5 in CDCl3.3 The 31P CP/MAS NMR spectrum of Silica-TRIP showed a

singlet signal at δ –52 (ppm) assignable to the P atom of the TRIP moiety (Figure 6a) (31P

NMR for 5; δ –54.9). The 13C CP/MAS spectrum showed a sharp signal at δ 2 ppm for the

Me carbons of the trimethylsilyl endcaps and multiple broad signals around δ 130 for the aromatic carbons of the TRIP moiety (Figure 6b). In the 29Si CP/MAS NMR spectrum

(Figure 6c), a weak signal at δ –36 was assigned to the bridgehead Si atom of the TRIP

moiety (29Si NMR for 5; δ –38.9).

55

(a)

(b)

(c)

Figure 6. CP/MAS NMR spectra of Silica-TRIP for (a) 31P (b) 13C and (c) 29Si nuclei.

56

The coordination property of Silica-TRIP in the reaction with [PdCl2(py)2] (py =

pyridine) was investigated. Specifically, the reaction of Silica-TRIP with an excess amount of

[PdCl2(py)2] (Pd/P 2:1) in CH2Cl2 at room temperature for 0.5 h produced pale yellow silica

gel, indicating that Pd atoms were bound to the gel. Unreacted [PdCl2(py)2] was recovered

from the filtrate, and its weight was measured. This procedure allowed us to estimate the

amount of P loading on the silica gel, which was calculated to be 0.078 mmol/g under the

assumption of selective formation of [PdCl2(py)(Silica-TRIP)] with a Pd/P stoichiometry of

1:1 (vide infra for the structure assignment). On the other hand, the inductively coupled

plasma-atomic emission spectroscopic (ICP-AES) analysis of [PdCl2(py)(Silica-TRIP)] gave

P and Pd loading values of 0.063 and 0.072 mmol/g, respectively. For convenience, the value

of 0.07 mmol/g was used for P loading in metal complexations and catalytic applications

(vide infra)

The 31P CP/MAS NMR spectrum of the silica-supported Pd complex obtained in this

manner showed a singlet peak at –5 ppm (Figure 7a). The comparison of this chemical shift

value with those of homogeneous Pd complexes prepared from TMSO-TRIP (5) (Pd/P 0:1,

1:1, 1:2 in Figure 8) is consisted with the formation of mono-P-ligated Pd complex

[PdCl2(py)(Silica-TRIP)] without forming a bis-P-ligated Pd complex PdCl2(Silica-TRIP)2

[31P NMR in CDCl3 for [PdCl2(py)(5)] δ –6.5; for [PdCl2(5)2] δ –19.5]. Notably, the mono-P-ligated Pd complex was formed selectively even when excess P was present (Pd/P

1:2, in CH2Cl2 at room temperature for 0.5 h) (Figure 7b).

57

(a)

(b)

Figure 7. 31P CP/MAS NMR spectra obtained from (a) PdCl2(py)2/Silica-TRIP (Pd/P 2:1)

and (b) PdCl2(py)2/Silica-TRIP (Pd/P 1:2).

58

Figure 8. 31P NMR spectra obtained from PdCl2(py)2 and TMSO-TRIP (5) [in CDCl3, Pd/P

(a) 0:1; (b) 1:1; (c) 1:2].

In contrast, the reaction of PdCl2(py)2 with silica-supported non-cage-type

triarylphosphine Silica-1p-TPP4h,15b (Pd/P 1:2, in CH2Cl2 at room temperature for 1 h) gave

well-separated two 31P signals at δ 29 and δ 23, which were assignable to a 1:1 Pd/P complex PdCl2(py)(Silica-1p-TPP) and a 1:2 Pd/P complex PdCl2(Silica-1p-TPP)2, respectively, on

the basis of the 31P NMR studies using the corresponding soluble phosphine

PPh2[4-Me2(iPrO)Si-C6H4] (6)15b (Pd/P 0:1, 1:1 or 1:2; in CDCl3, Figure 10), along with a

signal for the free phosphine at δ –4 (Figure 9).19 Comparison of the Pd coordination properties of Silica-TRIP and Silica-1p-TPP indicated that the cage-to-surface direct

immobilization was an effective means for site isolation of the P centers to allow selective

mono-P-ligation.

59

Figure 9. 31P CP/MAS NMR spectra obtained from PdCl2(py)2/Silica-1p-TPP (Pd/P 1:2).

Figure 10. 31P NMR spectra obtained from PdCl2(py)2 and PPh2[4-Me2(iPrO)Si-C6H4] [in

CDCl3, Pd/P (a) 0:1; (b) 1:1; (c) 1:2].

To demonstrate ligand characteristics of Silica-TRIP for catalytic applications, we

examined Pd-catalyzed Suzuki–Miyaura coupling of chloroarenes, in which mono-ligation of

two-electron donor ligands is important for high catalytic activity.10–12 Specifically, the

reaction of 4-chlorotoluene (7a, 0.5 mmol) and phenylboronic acid (8a, 0.6 mmol) was

conducted at 60 °C for 12 h in the presence of K3PO4 as a base and a palladium source (0.5

mol%). The results are summarized in Table 2.

The pre-formed immobilized mono-P-ligated Pd complex PdCl2(py)(Silica-TRIP)

60

initiated the coupling reaction to give the desired product 9a in 56% yield, regardless of the

moderate electron-donor power of Silica-TRIP as a triarylphosphine (Table 2, entry 1).

However, the heterogeneous catalyst prepared in-situ from PdCl2(py)2 and Silica-TRIP were

less efficient (5%, entry 2). In both cases, their solution phases changed from colorless to

dark brown during the reactions probably due to leaching of Pd. More active catalyst was

produced by a combination of Silica-TRIP and commercially available Pd(OAc)2 (93%, entry

3). The supernatant was colorless; however, 3% Pd leaching into solution was observed by

the ICP-AES analysis (vide infra). Using unmodified silica gel CARiACT Q10 or

TMS-endcapped CARiACT Q10 in place of Silica-TRIP under the conditions of entry 3

caused no reaction, indicating that Pd(OAc)2 directly bound to silica gel was not effective

(entries 4 and 5).

Table 2. Pd-catalyzed Suzuki–Miyaura cross-coupling between 7a and 8a.a

Me Cl Ph+

[Pd] (0.5 mol%)Additive

K3PO4 (1.5 mmol)THF, 60 °C, 12 h7a (0.5 mmol) 8a (0.6 mmol)

Me Ph

9a

(HO)2B

entry Pd source [Pd] additive yield (%)b

1 PdCl2(py)(Silica-TRIP) none 56

2c PdCl2(py)2 Silica-TRIP 5

3c Pd(OAc)2 Silica-TRIP 93 (88)

4d Pd(OAc)2 CARiACT Q10 (unmodified) 0

5d Pd(OAc)2 CARiACT Q10 (TMS-endcapped) 0

a Conditions: 7a (0.5 mmol), 8a (0.6 mmol), [Pd] (0.0025 mmol, 0.5 mol%), K3PO4 (1.5

mmol), THF (1.5 mL), 60 °C, 12 h. b Yields of 9a were determined by 1H NMR. Isolated

yield is given in parentheses. c Silica-TRIP (0.030 mmol, 0.6 mol%). d CARiACT Q10 (42.9

mg).

Effects of phosphine ligands shown in Figure 11 were investigated in the presence of a

catalytic amount of Pd(OAc)2 (0.5 mol%, Table 3). Cage-type trialkylphosphine

Silica-SMAP4 and tripodally immobilized triarylphosphine Silica-3p-TPP,15b which possess

mono-P-ligating features toward transition metals, promoted the coupling reaction, but their

61

reaction efficacies were slightly less than that of Silica-TRIP (Table 2, entry 3 vs. Table 3,

entries 1 and 2). The conventional monopodally silica-immobilized ligand Silica-1p-TPP, in

which site-isolation of the P center was not enough as shown in Figure 9, was much less

effective (9% yield, entry 3). In contrast to the silica-supported catalyst systems, their

homogeneous counterparts TMSO-TRIP (5), Ph-TRIP,4h Ph-SMAP,5 or PPh3 induced no or

trace of coupling reactions (entries 4–7). These results indicated that immobilization of

ligands for obtaining a mono-P-ligating feature (e.g., cage-to-surface or tripod), which was

supported by NMR studies of Pd-P coordination (Figure 7), is crucial for the high catalytic

activities obtained with Silica-TRIP. Under the present reaction conditions, sterically

demanding homogeneous trialkylphosphines such as PCy3 and PtBu3 were not as effective as

Silica-TRIP (entries 8 and 9), while a (dicyclohexylphosphino)biphenyl-type ligand

XPhos,10a which is one of the most efficient ligands reported to date in the cross-coupling

reactions, gave 9a quantitatively (entry 10)

Table 3. Ligand effects in Pd-catalyzed Suzuki–Miyaura cross-coupling between 7a and 8a.a

Me Cl Ph+

Pd(OAc)2 (0.5 mol%)Ligand (0.6 mol%)

K3PO4 (1.5 mmol)THF, 60 °C, 12 h7a (0.5 mmol) 8a (0.6 mmol)

Me Ph

9a

(HO)2B

entry ligand yield (%)b

1c Silica-SMAP 82d

2 Silica-3p-TPP 83

3 Silica-1p-TPP 9

4 TMSO-TRIP (5) 1

5 Ph-TRIP 0

6 Ph-SMAP 0

7 PPh3 <1

8 PCy3 51

9 PtBu3 14

10 XPhos >99 a Conditions: 7a (0.5 mmol), 8a (0.6 mmol), Pd(OAc)2 (0.0025 mmol, 0.5 mol%), ligand

(0.003 mmol, 0.6 mol%), K3PO4 (1.5 mmol), THF (1.5 mL), 60 °C, 12 h. b Yields of 9a were

determined by 1H NMR. c 0.5 mol% of ligand, for 10 h. d Data were taken from ref. 4g.

62

SiO2

OSiOO

O

SiOSiOO

O

SiMe3

Silica-1p-TPP

Me

Me

Ph2P

P

Si

Ph-TRIP

Si

P

Ph-SMAP XPhos

PCy2iPr iPr

iPr

SiO2

Silica-3p-TPP

P

Si

SiSi

OSi

MeMe

MeMe

MeMe

OSi

O

Si

O OO

O O

OO

O

O

OSiOO

O

SiMe3

Figure 11. Heterogeneous and homogeneous phosphine ligands employed in Table 3.

The heterogeneous Silica-TRIP-Pd catalyst has the advantage of catalyst-product

separation over homogeneous molecular catalyst systems. Thus, after the reaction between 7a

and 8a in the presence of the Silica-TRIP/Pd(OAc)2 catalyst system (Table 2, entry 3), the

reaction mixture was filtered through Celite®. The ICP-AES analysis indicated that Pd

residues in the filtrate were 3% of the loaded Pd. This value was much less than the

corresponding value (58% of the loaded Pd) in the experiment for the homogeneous system

with the XPhos ligand (Table 3, entry 10).

Unfortunately, reusability of the Silica-TRIP/Pd(OAc)2 catalyst system was

unsatisfactory under the present conditions. Specifically, the reaction of 7a (0.5 mmol) and

8a (0.75 mmol) with K3PO4 (1.5 mmol) in THF (1 mL) at 60 °C for 1 h in the presence of a

heterogeneous catalyst prepared from Pd(OAc)2 (1 mol%) and Silica-TRIP (1.5 mol%) gave

9a in 97% yield (1H NMR). Insoluble solids were recovered by filtration through a cotton

plug followed by washing successively with H2O, THF, and Et2O. The catalysts recovered in

this way gave decreased product yields with the increasing of the reuse (2nd run, 28%; 3rd

run, 3%). The black color of the solid phase was supportive of the formation of inactive Pd

species in the solid phase. Gradual Pd leaching was also observed during the catalyst reuse

experiment; during the second run, the solution phase turned dark brown. This Pd leaching

may be due to the moderate coordination ability of the triarylphosphine center of

Silica-TRIP.

The 31P CP/MAS NMR spectrum of the silica gel Pd-Silica-TRIP recovered after the

coupling reaction on a larger scale (7a; 2.5 mmol) showed a distinct major signal at δ 4

63

together with minor signals at δ −52 (Silica-TRIP) and −8 (overlapped with Silica-TRIP

oxide) (Figure 12).

Figure 12. 31P CP/MAS NMR spectra of the recovered silica gel after the reaction of 7a and

8a with the Silica-TRIP/Pd(OAc)2 catalyst system.

On the other hand, a sample obtained from the solution phase of the reaction mixture

showed no signal in 31P NMR spectroscopy (in CDCl3). These results indicate that at least

most of the phosphine moiety remained bound to the solid surface. However, partial

degradation of the Silica-TRIP structure during the catalytic reaction cannot be ruled out.

3. Conclusion

A silica-supported triptycene-type phosphine Silica-TRIP, comprising a

9-phospha-10-silatriptycene (TRIP) and silica gel as a coordinating moiety and a solid

support, respectively, was synthesized. This material was characterized by nitrogen

adsorption measurements and 13C, 29Si and 31P CP/MAS NMR spectroscopies. Because of the

cage-to-surface direct immobilization, Silica-TRIP exhibited a mono-P-ligating feature

toward a Pd(II) complex, resulting in selective formation of a 1:1 Pd-P species even with the

P-ligand in excess. This coordination behavior was confirmed by 31P CP/MAS NMR

spectroscopy. The use of Silica-TRIP as a ligand enabled the Pd-catalyzed Suzuki–Miyaura

cross-coupling reaction with chloroarenes under mild conditions, regardless of the moderate

electron-donating nature of the triarylphosphine-based ligand. The facile catalyst-product

separation by filtration was demonstrated as the merit of the heterogeneous Pd catalyst

system over homogeneous systems. However, catalyst deactivation in the Suzuki–Miyaura

64

coupling hampered the efficient reuse of the Pd catalyst.


4.1. Instrumentation and Chemicals

All reactions were carried out under nitrogen or argon atmosphere. Materials were

obtained from commercial suppliers or prepared according to standard procedures unless

otherwise noted. Although Silica-SMAP4a,c and Silica-TRIP4h are commercially available, the

silica-supported ligands for this work were prepared according to the reported procedure or

the modified procedure described below, respectively. CARiACT Q-10 silica gel (Catalyst

grade, 75–150 µm, Fuji Silysia Chemical, Ltd.) was dehydrated by heating at 120 °C under

vacuum for 10 h and stored in a glove box before use. Silica-3p-TPP,15b Silica-1p-TPP,15b

Ph-SMAP,5 and Ph-TRIP4h were prepared according to the reported procedure. Pd(OAc)2 was

purchased from Aldrich Co., Ltd., and PdCl2(py)2 was prepared according to the literature.20

Phenylboronic acid (8a) was purchased from TCI Co., Ltd., and was recrystallized from hot

water before use. K3PO4 was purchased from Junsei Chemicals Co., Ltd., and dried at 150 °C

for 10 h under vacuum. All solvents for catalytic reactions were degassed via three

freeze–pump–thaw cycles.

Solution NMR spectra were recorded on a JEOL ECX-II (400 MHz for 1H NMR, 100.5

MHz for 13C NMR, 79.4 MHz for 29Si NMR and 161.8 MHz for 31P NMR). Chemical shift

values are referenced to Me4Si (1H and 29Si), the residual solvent (13C), and H3PO4 (31P).

Magic angle spinning (MAS) NMR spectra were recorded on a Bruker MSL-300

spectrometer, operating at 75.5 MHz for 13C NMR, 59.6 MHz for 29Si NMR, and 121.5 MHz

for 31P NMR. Combustion elemental analyses (J-SCIENCE Micro Corder JM10 or Yanako

MT-6) and high-resolution mass spectra (Thermo Scientific Exactive or JEOL JMS-T100LC

for ESI-MS, and JEOL JMS-T100GCv for EI-MS) were recorded at the Instrumental

Analysis Division, Equipment Management Center, Creative Research Institution, Hokkaido

University. N2 adsorption (Quantachrome Autosorb-6) and ICP-AES analysis (Shimadzu

ICPE-9000) were performed at Hokkaido University Sousei Hall. A microwave digestion

system (Milestone, ETHOS One) was used to prepare samples for ICP-AES analysis. IR

spectra were measured with a Perkin-Elmer Spectrum One. GLC analyses were conducted on

a Shimadzu GC-14B equipped with a flame ionization detector. Melting points were

determined on a micro melting point apparatus (Yanaco MP-500D).

65


Preparation of Tris(2-bromophenyl)phosphine (2).6a A solution of iPrMgBr in THF (0.92

M, 38 mL, 35 mmol), which was freshly prepared from iPrBr and Mg, was added over 25

min to a solution of 1-bromo-2-iodobenzene (1, 9.90 g, 35 mmol) in THF (35 mL) at –20 °C.

The reaction mixture turned into a gray slurry after stirring at –20 °C for an additional 3 h.

After complete consumption of 1, which was confirmed by GC analysis of a small aliquot of

the reaction mixture, TMEDA (5.25 mL, 35 mmol) and PCl3 (872 µL, 10 mmol) were added

in a dropwise manner in that order at –20 °C. The resulting mixture was allowed to warm to

0 °C and stirred at this temperature for an additional 14 h to give a clear pale-yellow solution.

After quenching with NH4Cl aq. at 0 °C, the reaction mixture was extracted with EtOAc. The

organic layer was washed with brine, dried over MgSO4, filtered, and concentrated. The

residue was passed through a short silica gel column with toluene as an eluting solvent, and

the eluent was evaporated under vacuum. The residual solids were recrystallized from

benzene/MeOH to give tris(2-bromophenyl)phosphine as a while solid (2.86 g, 57% yield). 1H NMR (CDCl3): δ 6.74–6.77 (m, 3H), 7.22–7.28 (m, 6H), 7.63–7.66 (m, 3H). 13C NMR

(CDCl3): δ 127.78, 130.37 (d, J = 34.4 Hz), 130.73, 133.19 (d, J = 1.9 Hz), 134.69, 136.72 (d,

J = 11.5 Hz). 31P NMR (CDCl3): δ –2.8.

Preparation of Silanol 3. For the preparation of 3, Tsuji and Tamao’s procedure for the

synthesis of 10-chloro-9-phospha-10-silatriptycene6a was modified as follows. A solution of

tBuLi in pentane (1.77 M, 5.1 mL, 9.0 mmol) was added over 15 min to a solution of 2 (748

mg, 1.5 mmol) in THF (4.5 mL) and Et2O (23 mL) at –78 °C. After stirring for 4 h, SiCl4

(172 µL, 1.5 mmol) was added in a dropwise manner at –78 °C, and the resulting mixture

was stirred at this temperature for an additional 4 h. After quenching the excess

organolithium species with Me3SiCl (1.1 mL, 9 mmol) at –78 °C, the mixture was allowed to

warm to room temperature and stirred for an additional 13 h. After evaporation of the

volatiles, the residue was dissolved in toluene and filtered through a Celite® pad. The filtrate

was concentrated, and the crude product was purified by silica gel column chromatography

(hexane/EtOAc 100:0–80:20) followed by reprecipitation from CH2Cl2/hexane to give silanol

3 as a white solid (321 mg, 70% yield). Single crystals of 3 suitable for X-ray diffraction

studies were obtained by recrystallization from a CHCl3/hexane solution (CCDC: 1060983).

M.p.: 120 °C (decomp.). 1H NMR (CDCl3): δ 3.32 (s, 1H), 7.21–7.28 (m, 6H), 7.81 (d, J =

6.4 Hz, 3H), 7.87 (dd, J = 10.8, 7.2 Hz, 3H). 13C NMR (CDCl3): δ 127.86, 128.10 (d, J = 15.2

Hz), 131.56, 134.69 (d, J = 45.8 Hz), 141.13, 146.12 (d, J = 8.6 Hz). 29Si NMR (CDCl3): δ

–30.6 (d, J = 8.5 Hz). 31P NMR (CDCl3): δ –54.0. IR (ATR): 3347 (br), 3052, 2964, 1688,

66

1572, 1430, 1260, 896, 755, 666 cm–1. HRMS–ESI (m/z): [M–H]– calcd for C18H12OPSi,

303.04005; found, 303.04086.

Preparation of Disiloxane 4. Silanol 3 (30.0 mg, 0.1 mmol) and imidazole (1.4 mg, 0.02

mmol) were dissolved in benzene (0.5 mL), and the mixture was stirred at 80 °C for 10.5 h.

After cooling to room temperature, the insoluble solids were filtered and washed with

benzene to give the disiloxane 4 as a white solid (15.0 mg, 52% yield). Due to the low

solubility of 4 into organic solvents, clear NMR data were not obtained.

White solid. M.p. 430 °C (decomp.). 1H NMR (CDCl3): δ 7.22–7.26 (m, 6H), 7.31 (t, J = 7.2

Hz, 6H), 7.91 (d, J = 6.4 Hz, 6H), 7.98 (dd, J = 11.2, 7.2 Hz, 6H). 13C NMR (CDCl3): δ

128.27, 128.47 (d, J = 15.3 Hz), 131.77, 134.98 (d, J = 45.8 Hz), 140.77, 146.31 (d, J = 9.6

Hz). 31P NMR (CDCl3): δ –55.1. HRMS-EI (m/z) Calcd for [M]+ C36H24OP2Si2, 590.08409;

found, 590.08389.

Preparation of TMSO-TRIP 5. A solution of silanol 3 (45.7 mg, 0.15 mmol) in CH2Cl2 (2

mL) was added dropwise to a solution of N-trimethylsilylimidazole (105 mg, 0.75 mmol) in

CH2Cl2 (2 mL). After stirring at room temperature for 1 h, MeOH (2 mL) was added to

quench the excess N-trimethylsilylimidazole, and then the mixture was stirred for additional

10 min. The volatiles were removed under reduced pressure. The crude product was purified

by silica gel column chromatography (eluting with CH2Cl2) to give

10-{(trimethylsilyl)oxy}-9-phospha-10-silatriptycene (5) as a white solid (49.0 mg, 87%

yield).

M.p.: 225–228 ºC. 1H NMR (CDCl3): δ 0.52 (s, 9H), 7.19–7.28 (m, 6H), 7.76 (dd, J = 6.8,

0.8 Hz, 3H), 7.85 (dd, J = 11.6, 6.8 Hz, 3H). 13C NMR (CDCl3): δ 2.48, 127.79–127.94 (m),

131.58, 134.61 (d, J = 45.8 Hz), 142.09, 146.12 (d, J = 7.6 Hz). 31P NMR (CDCl3): δ –54.9. 29Si NMR (CDCl3): δ –38.9 (d, J = 9.1 Hz), 14.4. HRMS-EI (m/z) Calcd for [M]+

C21H21OPSi2, 376.08685; found, 376.08541.

Preparation of Silica-TRIP. Silanol 3 (365 mg, 1.2 mmol), CARiACT Q-10 silica gel (10.6

g), imidazole (408 mg, 6.0 mmol), and anhydrous, degassed toluene (42 mL) were placed in a

200-mL three-necked flask equipped with a mechanical stirrer under argon atmosphere. The

suspension was gently stirred at 100 °C for 16 h. After cooling to room temperature, the

mixture was filtered, washed successively with degassed toluene, toluene-MeOH (1:1), and

MeOH, and dried under vacuum at 120 °C overnight. Next, a solution of

N-trimethylsilylimidazole (5.3 mL) in THF (30 mL) was added to the flask with the

functionalized silica gel Silica-TRIP(SiOH). The suspension was stirred at 60 °C for 24 h

under argon atmosphere. After cooling to room temperature, solids were collected by

filtration through a glass filter, washed with MeOH, and dried under vacuum at 120 °C

67

overnight to give 9.4 g of Silica-TRIP. 13C CP/MAS NMR: δ 2, 123–150 (br-m). 29Si CP/MAS NMR: δ –110, −102, –36, 14. 31P

CP/MAS NMR: δ –52. Elemental Anal. found: C 5.33; H 1.19.

Reaction of PdCl2(py)2 and Silica-TRIP (Pd/P 2:1). Silica-TRIP (401.5 mg, 0.028 mmol,

0.07 mmol/g) and PdCl2(py)2 (18.8 mg, 0.056 mmol) were placed in a vial containing a

magnetic stirring bar. Anhydrous, degassed CH2Cl2 (2 mL) was added, and the tube was

sealed with a screw cap. The mixture was stirred at room temperature for 0.5 h. The

suspension was filtered and washed with CH2Cl2. The filtrate was evaporated to recover

unreacted PdCl2(py)2 (8.3 mg, 0.025 mmol). The pale yellow silica gel was dried under

vacuum to give PdCl2(py)(Silica-TRIP) (375.1 mg). Thus, P loading on Silica-TRIP was

calculated to be 0.078 mmol/g based on a Pd to P stoichiometry of 1:1

[{(18.8–8.3)/335.53}/0.4015 = 0.078]. For convenience, the value of 0.07 mmol/g was used

for P loading in metal complexations and catalytic applications. 13C CP/MAS NMR: δ 3, 120–158 (br-m). 31P CP/MAS NMR: δ –5.

Reaction of PdCl2(py)2 and Silica-TRIP (Pd/P 1:2). Silica-TRIP (399.2 mg, 0.028 mmol,



sealed with a screw cap. The mixture was stirred at room temperature for 0.5 h. The

suspension was filtered and washed with CH2Cl2. The pale yellow silica was dried under

vacuum to give a mixture of PdCl2(py)(Silica-TRIP) and unreacted Silica-TRIP (363.5 mg). 31P CP/MAS NMR: δ –52, –5.

Reaction of PdCl2(py)2 and TMSO-TRIP (Pd/P 1:1, 1:2). TMSO-TRIP (5) (0.02 mmol)

and PdCl2(py)2 (0.02 mmol for Pd/P 1:1; 0.01 mmol for Pd/P 1:2) were placed in a 5-mL

glass tube containing a magnetic stirring bar. CDCl3 (0.7 mL) was added and stirred at room

temperature for 5 min. The mixture was analyzed with 31P NMR spectroscopy.

Preparation of PdCl2(py)(5). A solution of 5 (18.8 mg, 0.05 mmol) in CHCl3 (1.5 mL) was

added dropwise to a solution of PdCl2(py)2 (17.8 mg, 0.05 mmol) in CHCl3 (1.5 mL). The

mixture was stirred at room temperature for 0.5 h. The volatiles were evaporated. The residue

was extracted with benzene. After filtration, the solution was evaporated. The residue was

recrystallized from CHCl3/hexane to give PdCl2(py)(5) as a yellow solid (22.8 mg,

contaminated with 3% of PdCl2(py)2, 71% yield)

M.p.: 190 °C (decomp.). 1H NMR (CDCl3): δ 0.53 (s, 9H), 7.30–7.39 (m, 6H), 7.50 (t, J = 7.2

Hz, 2H), 7.71 (d, J = 6.8 Hz, 3H), 7.88 (t, J = 7.2 Hz, 1H), 9.12 (dd, J = 13.6, 7.3 Hz, 3H),

9.16–9.19 (m, 2H). 13C NMR (CDCl3): δ 2.37, 124.89 (d, J = 3.8 Hz), 127.96 (d, J = 13.4 Hz),

128.73, 130.49 (d, J = 7.6 Hz), 136.74 (d, J = 19.2 Hz), 138.57, 140.04 (d, J = 49.8 Hz),

68

140.99, 151.47. 31P NMR (CDCl3): δ –6.5. Attempts to obtain MS spectra (ESI or FAB) of

PdCl2(py)(5) were unsuccessful.

Preparation of PdCl2(5)2. The mixture of 5 (37.6 mg, 0.10 mmol), PdCl2(py)2 (17.8 mg,

0.05 mmol) and CHCl3 (2 mL) was stirred at room temperature for 1 h. The volatiles were

evaporated. The residue was washed with CHCl3 to give PdCl2(5)2 as a yellow solid (39.6 mg,

43% yield).

M.p.: 310 ºC (decomp.). 1H NMR (CDCl3): δ 0.55 (s, 18H), 7.30–7.43 (m, 12 H), 7.78 (d, J =

7.6 Hz, 6H), 9.18–9.24 (m, 6H). 31P NMR (CDCl3): δ –19.5. HRMS-ESI (m/z) Calcd for

[M+Na]+ C42H42Cl2O2P2PdSi4Na, 953.00508; found 953.00236. 13C NMR data are not

available due to the low solubility of PdCl2(5)2 in organic solvents.

Reaction of PdCl2(py)2 and Silica-1p-TPP (Pd/P 1:2). Silica-1p-TPP (200 mg, 0.018 mmol,



sealed with a screw cap. The mixture was stirred at room temperature for 1 h. The suspension

was filtered and washed with CH2Cl2. The pale yellow silica was dried under vacuum to give

a mixture of PdCl2(py)(Silica-1p-TPP), PdCl2(Silica-1p-TPP)2 and unreacted Silica-TRIP

(200 mg). 31P CP/MAS NMR: δ –4, 23, 29.

Reaction of PdCl2(py)2 and PPh2[4-Me2(iPrO)Si-C6H4] (Pd/P 1:1, 1:2).

PPh2[4-Me2(iPrO)Si-C6H4] (6) (0.02 mmol) and PdCl2(py)2 (0.02 mmol for Pd/P 1:1; 0.01

mmol for Pd/P 1:2) were placed in a 5-mL glass tube containing a magnetic stirring bar.

CDCl3 (0.7 mL) was added and stirred at room temperature for 5 min. The mixture was

analyzed with 31P NMR spectroscopy.

Preparation of PdCl2(py)(6). A solution of 6 (18.9 mg, 0.05 mmol) in CHCl3 (1.5 mL) was

added dropwise to a solution of PdCl2(py)2 (17.8 mg, 0.05 mmol) in CHCl3 (1.5 mL). The

mixture was stirred at room temperature for 0.5 h. The volatiles were evaporated. The residue

was extracted with benzene. After filtration, the solution was evaporated. The residue was

recrystallized from benzene/hexane to give PdCl2(py)(6) as a yellow solid (16.8 mg,

contaminated with 6% of PdCl2(py)2, 51% yield)

M.p.: 210 °C (decomp.). 1H NMR (CDCl3): δ 0.37 (s, 6H), 1.15 (d, J = 6.4 Hz, 6H), 4.02

(sept, J = 6.4 Hz, 1H), 7.35–7.51 (m, 8H) 7.64 (dd, J = 8.4, 2.8 Hz, 2H), 7.76–7.84 (m, 7H),

8.99–9.01 (m, 2H). 13C NMR (CDCl3): δ –1.16, 25.68, 65.51, 124.59 (d, J = 2.8 Hz), 128.09

(d, J = 11.5 Hz), 129.21 (d, J = 58.4 Hz), 130.16 (d, J = 56.5 Hz), 131.02 (d, J = 2.8 Hz),

133.02 (d, J = 10.6 Hz), 133.90 (d, J = 9.5 Hz), 134.82 (d, J = 9.5 Hz), 138.20, 142.33 (d, J =

1.9 Hz), 151.60. 31P NMR (CDCl3): δ 29.3. Attempts to obtain MS spectra (ESI or FAB) of

69

PdCl2(py)(6) were unsuccessful.

Preparation of PdCl2(6)2. The mixture of 6 (22.7 mg, 0.06 mmol), PdCl2(py)2 (10.1 mg,

0.03 mmol) and CHCl3 (1 mL) was stirred at room temperature for 1 h. The volatiles were

evaporated. The resulting residue was recrystallized from CH2Cl2/hexane to give PdCl2(6)2 as

a yellow solid (26.5 mg, contaminated with traces of impurities, 47% yield,)

M.p.: 192–195 °C. 1H NMR (CDCl3): δ 0.36 (s, 12H), 1.14 (d, J = 6.4 Hz, 12H), 4.01 (sept, J

= 6.4 Hz, 2H), 7.35–7.45 (m, 12H), 7.59 (d, J = 7.6 Hz, 4H), 7.68–7.73 (m, 12H). 13C NMR

(CDCl3): δ –1.15, 25.68, 65.44, 128.03 (vt, J = 4.8 Hz), 129.51 (vt, J = 24.9 Hz), 130.48,

130.59 (vt, J = 23.9 Hz), 132.97 (vt, J = 4.8 Hz), 134.15 (vt, J = 5.7 Hz), 135.00 (vt, J = 6.7

Hz), 141.48. 31P NMR (CDCl3): δ 23.7. HRMS-ESI (m/z) Calcd for [M+Na]+

C46H54Cl2O2P2PdSi2Na, 957.14513; found 957.14797.

Typical Procedure for the Suzuki–Miyaura Coupling Reaction. In a nitrogen-filled glove

box, Silica-TRIP (0.07 mmol/g, 42.9 mg, 0.003 mmol) and a solution of Pd(OAc)2 (0.56 mg,

0.0025 mmol) in anhydrous, degassed THF (0.5 mL) were placed in a 10-mL glass tube

containing a magnetic stirring bar. After stirring at room temperature for 5 min,

phenylboronic acid (8a, 73.1 mg, 0.6 mmol), K3PO4 (318 mg, 1.5 mmol), p-chlorotoluene (7a,

63.3 mg, 0.5 mmol), and THF (1 mL) were added successively. The tube was sealed with a

screw cap and removed from the glove box. The mixture was stirred at 60 °C for 12 h. After

cooling to room temperature, the mixture was diluted with Et2O and filtered through a Celite®

pad (eluting with Et2O). The volatiles were evaporated, and an internal standard

(1,1,2,2-tetrachloroethane) was added to determine the yield of 4-methylbiphenyl (9a, 93%

yield). The crude product was purified by silica gel chromatography (eluting with hexane) to

give 9a (74.3 mg, 0.44 mmol, 88% yield).

ICP-AES Measurements for Pd Residue. After the reaction of 7a (0.5 mmol) and 8a (0.6

mmol) in the presence of 0.5 mol% the Silica-TRIP-Pd catalyst (Table 2, entry 3), the

reaction mixture was diluted with Et2O, and filtered through a Celite® pad (eluting with Et2O).

The volatiles were evaporated. A small aliquot of the residue (ca. 5 mg) was taken for a

microwave-assisted acid digestion with aqua regia (1000 W, 220 °C) followed by a mixture

of nitric acid and perchloric acid (1000 W, 220 °C). The resulting mixture was diluted in H2O

(20 mL). This solution was subjected to ICP-AES analysis.

X-ray Crystallographic Analysis of 3. Crystal data for 3{3·1/3(CHCl3)} (CCDC 1060983;

recrystallization from CHCl3/hexane). C55H40Cl3O3P3Si3, M = 1032.46, trigonal, space group

P3––c1 (#165), a = 15.5297(5) Å, c = 24.1564(11) Å, V = 5045.3(4) Å3, Z = 4, density (calc.) =

1.359, total reflections collected = 39823, unique reflections = 3860 (Rint = 0.0542), GOF =

1.139, R1 (I>2σ(I)) = 0.0461, wR2 = 0.1077.

70

Data were collected on a Rigaku Mercury 70 CCD diffractometer with graphite

monochromated Mo-Kα radiation (λ = 0.71075 Å) at 150 K, and processed using the

CrystalClear software.21 Structures were solved by a direct method using SIR-2004,22 and

refined by full-matrix least-square method using SHELXL-97.23 Non-hydrogen atoms were

refined anisotropically. All hydrogen atoms except for the silanol protons were located on the

calculated positions and refined using a riding model. The silanol protons (H1 and H2;

disordered, 1:1) were located in the difference Fourier map and refined isotropically. All

calculations were performed using the CrystalStructure software package.24

5. References

(1) (a) Lindner, E.; Schneller, T.; Auer, F.; Mayer, H. A. Angew. Chem., Int. Ed. 1999, 38,

2154–2174. (b) Wight, A. P.; Davis, M. E. Chem. Rev. 2002, 102, 3589–3614. (c)

Corma, A.; Garcia, H. Adv. Synth. Catal. 2006, 348, 1391–1412. (d) Hoffmann, F.;

Cornelius, M.; Morell, J.; Fröba, M. Angew. Chem., Int. Ed. 2006, 45, 3216–3251. (e)

Opanasenko, M.; Štěpnička, P.; Čejka, J. RSC Adv. 2014, 4, 65137–65162.

(2) (a) Recoverable and Recyclable Catalysts; Benaglia, M. Ed.; Wiley: Chichester, 2009;

(b) Heterogenized Homogeneous Catalysts for Fine Chemicals Production: Materials

and Processes; Barbaro, P.; Liguori, F. Eds.; Springer: Dordrecht, 2010.

(3) Blümel, J. Coord. Chem. Rev. 2008, 252, 2410–2423.

(4) Hamasaka, G.; Ochida, A.; Hara, K.; Sawamura, M. Angew. Chem., Int. Ed. 2007, 46,

5381–5383. (b) Kawamorita, S.; Hamasaka, G.; Ohmiya, H.; Hara, K.; Fukuoka, A.;

Sawamura, M. Org. Lett. 2008, 10, 4697–4700. (c) Hamasaka, G.; Kawamorita, S.;

Ochida, A.; Akiyama, R.; Hara, K.; Fukuoka, A.; Asakura, K.; Chun, W. J.; Ohmiya,

H.; Sawamura, M. Organometallics 2008, 27, 6495–6506. (d) Kawamorita, S.; Ohmiya,

H; Hara, K.; Fukuoka, A.; Sawamura, M. J. Am. Chem. Soc. 2009, 131, 5058–5059. (e)

Kawamorita, S.; Ohmiya, H.; Sawamura, M. J. Org. Chem. 2010, 75, 3855–3858. (f)

Yamazaki, K.; Kawamorita, S.; Ohmiya, H.; Sawamura, M. Org. Lett. 2010, 12,

3978–3981. (g) Kawamorita, S.; Ohmiya, H.; Iwai, T.; Sawamura, M. Angew. Chem.,

Int. Ed. 2011, 50, 8363–8366. (h) Kawamorita, S.; Miyazaki, T.; Ohmiya, H.; Iwai, T.;

Sawamura, M. J. Am. Chem. Soc. 2011, 133, 19310–19313. (i) Kawamorita, S.;

Yamazaki, K.; Ohmiya, H.; Iwai, T.; Sawamura, M. Adv. Synth. Catal. 2012, 354,

3440–3444. (j) Kawamorita, S.; Murakami, R.; Iwai, T.; Sawamura, M. J. Am. Chem.

Soc. 2013, 135, 2947–2950. (k) Konishi, S.; Kawamorita, S.; Iwai, T.; Steel, P. G.;

Marder, T. B.; Sawamura, M. Chem. Asian J. 2014, 9, 434–438. (l) Murakami, R.;

Tsunoda, K.; Iwai, T.; Sawamura, M. Chem. Eur. J. 2014, 20, 13127–13131.

71





(6) (a) Tsuji, H.; Inoue, T.; Kaneta, Y.; Sase, S.; Kawachi, A.; Tamao, K. Organometallics

2006, 25, 6142–6148. (b) Tsuji, H.; Inoue, T.; Sase, S.; Tamao, K. Acta Cryst. E 2006,

62, m535–m537.

(7) Kawamorita, S.; Miyazaki, T.; Iwai, T.; Ohmiya, H.; Sawamura, M. J. Am. Chem. Soc.

2012, 134, 12924–12927.

(8) Portions of this work on the synthesis of Silica-TRIP (ref. 4h) and its application to

Pd-catalyzed Suzuki–Miyaura cross-coupling of chloroarenes (ref. 16b) have been

reported.

(9) For selected reviews, see: Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed. 2002, 41,

4176–4211. (b) Suzuki, A. Angew. Chem., Int. Ed. 2011, 50, 6722–6737.

(10) For selected reviews, see: (a) Martin, R.; Buchwald, S. L. Acc. Chem. Res. 2008, 41,

1461–1473. (b) Fu, G. C. Acc. Chem. Res. 2008, 41, 1555–1564. (c) Fleckenstein, C.

A.; Plenio, H. Chem. Soc. Rev. 2010, 39, 694–711. (d) Lundgren, R. J.; Hesp, K. D.;

Stradiotto, M. Synlett 2011, 2011, 2443–2458. (e) Wong, S. M.; So, C. M.; Kwong, F.

Y. Synlett 2012, 2012, 1132–1153.

(11) For selected reviews, see: (a) Kantchev, E. A. B.; O’Brien, C. J.; Organ, M. G. Angew.

Chem., Int. Ed. 2007, 46, 2768–2813. (b) Fortman, G. C.; Nolan, S. P. Chem. Soc. Rev.

2011, 40, 5151–5169.

(12) For selected examples, see: (a) Iwasawa, T.; Komano, T.; Tajima, A.; Tokunaga, M.;

Obora, Y.; Fujihara, T.; Tsuji, Y. Organometallics 2006, 25, 4665–4669. (b) Ohta, H.;

Tokunaga, M.; Obora, Y.; Iwai, T.; Iwasawa, T.; Fujihara, T.; Tsuji, Y. Org. Lett. 2007,

9, 89–92. (c) Fujihara, T.; Yoshida, S.; Ohta, H.; Tsuji, Y. Angew. Chem., Int. Ed. 2008,

47, 8310–8314. (d) Snelders, D. J. M.; van Koten, G.; Gebbink, R. J. M. K. J. Am.

Chem. Soc. 2009, 131, 11407–11416. (e) Mom, S.; Beaupérin, M.; Roy, D.; Royer, S.;

Amardeil, R.; Cattey, H.; Doucet, H.; Hierso, J.-C. Inorg. Chem. 2011, 50,

11592–11603. (f) Chow, W. K.; Yuen, O. Y.; So, C. M.; Wong, W. T.; Kwong, F. Y. J.

Org. Chem. 2012, 77, 3543–3548. (g) Zhnag, J.; Bellomo, A.; Trongsiriwat, N.; Jia, T.;

Carroll, P. J.; Dreher, S. D.; Tudge, M. T.; Yin, H.; Robinson, J. R.; Schelter, E. J.;

Walsh, P. J. J. Am. Chem. Soc. 2014, 136, 6276–6287.

(13) Li, B.; Guan, Z.; Wang, W.; Yang, X.; Hu, J.; Tan, B.; Li, T. Adv. Mater. 2012, 24,

3390–3395.

72

(14) For related studies using phosphine-containing organic polymers, which were effective

for Pd-catalyzed Suzuki–Miyaura coupling of chloroarenes, see: (a) Hu, Q.-S.; Lu, Y.;

Tang, Z.-Y.; Yu, H.-B. J. Am. Chem. Soc. 2003, 125, 2856–2857. (b) Yamamoto, T.;

Akai, Y.; Nagata, Y.; Suginome, M. Angew. Chem., Int. Ed. 2011, 50, 8844–8847.

(15) (a) Iwai, T.; Harada, T.; Hara, K.; Sawamura, M. Angew. Chem., Int. Ed. 2013, 52,

12322–12326. (b) Iwai, T.; Tanaka, R.; Harada, T.; Sawamura, M. Chem. Eur. J. 2014,

20, 1057–1065. (c) Iwai, T.; Harada, T.; Tanaka, R.; Sawamura, M. Chem. Lett. 2014,

43, 584–586.

(16) Kowada, T.; Yamaguchi, S.; Ohe, K. Org. Lett. 2010, 12, 296–299.

(17) Single-crystal X-ray diffraction analysis of triorganosilanols with hydrogen-bonding

network: Beckmann, J.; Duthie, A.; Reeske, G.; Schürmann, M. Organometallics 2004,

23, 4630–4635.

(18) Without imidazole as an additive, a significant amount of silanol 3 remained in the

crude product (ca. 20% conversion of 3 after 12 h).

(19) The coordination behavior of Silica-1p-TPP toward a Pd(II) center using PdCl2(PhCN)2

was studied previously. See, ref 15b.

(20) Krogul, A.; Cedrowski, J.; Wiktorska, K.; Ozimiński, W. P.; Skupińska, J.; Litwinienko,

G. Dalton Trans. 2012, 41, 658–666.

(21) CrystalClear: (a) Rigaku Corporation, 1999. (b) CrystalClear Software User’s Guide,

Molecular Structure Corporation, 2000. (c) Pflugrath, J. W. Acta Cryst. D 1999, 55,

1718–1725.

(22) SIR-2004: Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.;

De Caro, L.; Giacovazzo, C.; Polidori, G.; Spagna, R. J. Appl. Cryst. 2005, 38,

381–388.

(23) SHELXL-97: Sheldrick, G. M. Acta Cryst. A 2008, 64, 112–122.

(24) CrystalStructure 4.0: Crystal Structure Analysis Package; Rigaku Corporation: Tokyo,

Japan, 2000–2010.

74

Chapter 3

Synthesis, Properties and Catalytic Application of a Triptycene-Type Anionic Borate-Phosphine Ligand

A borate-containing caged triarylphosphine L-X (X = Na or NBu4), featuring a

9-phospha-10-boratriptycene framework, was synthesized and characterized by NMR

spectroscopy and X-ray diffraction analysis. The NMR coupling constant of the

corresponding phosphine selenide indicated a higher electron-donating property of

borate-phosphine L compared to that of the 9-phospha-10-silatriptycene derivative (Ph-TRIP).

The coordination property of L-X to [PdCl(η3-allyl)] was dependent on the counter cation,

giving a neutral Pd complex [PdCl(η3-allyl)(L-NBu4)] from L-NBu4 in CH2Cl2 or a

zwitterionic Pd complex [Pd(η3-allyl)(MeCN)(L)] from L-Na in MeCN/CH2Cl2. Utility of L-X as a ligand for metal catalysis was demonstrated in the Pd-catalyzed Suzuki–Miyaura

cross-coupling of aryl chlorides.

75

1. Introduction

Caged phosphines with a bridgehead P atom are unique class of ligands in coordination and

organometallics chemistries.1,2 Due to their rigid structures, the P lone pair coordination is

highly oriented. Sawamura et al. developed caged phosphine compounds containing a

bridgehead silicon atom such as 1-phospha-4-silabicyclo[2.2.2]octanes (SMAP, named after

silicon-constrained monodentate trialkylphosphines, Figure 1a)3 and

9-phospha-10-silatriptycenes (TRIP, Figure 1b).4,5 Substituents at the bridgehead Si atom of

the SMAP derivatives had significant impact on electron-donor power of the P lone pair due

to long range orbital interactions in the rigid cage system.3b Furthermore, the Si atoms of the

caged phosphine molecules could be used as handles for immobilization of the phosphine

molecules on solid supports such as silica gel4,6 or gold surfaces.7

R

P

SiSi

P

R

(a) (b)

(R = Ph; Ph-SMAP) (R = Ph; Ph-TRIP) Figure 1. (a) SMAP and (b) TRIP molecules

In this context, the Si atoms of these silicon-containing caged phosphines was replaced

with a tetravalent B atom to produce anionic caged phosphine molecules8,9 that increase the

electron-donor power of the P lone pair.10 It is also expected that such borate-phosphine

hybrid ligands produce zwitterionic organometallic species with a well-defined location of

cation and anion centers upon binding to cationic metal species.11

This chapter describes the synthesis and characterization of a borate-containing caged

triarylphosphine (L-X) featuring a 9-phospha-10-boratriptycene framework (Figure 2). The P

lone pair in the borate-phosphine L-X has a higher electron-donor power compared to the

corresponding silicon-containing caged phosphine (Ph-TRIP, Figure 1). A zwitterionic Pd(II)

complex with the cationic metal center and the anionic caged borate-phosphine (L) was also

synthesized and characterized. The newly developed caged borate-phosphine L-X enabled

the Pd-catalyzed Suzuki–Miyaura cross-coupling of aryl chlorides under mild conditions, for

which neither the Si-analog Ph-TRAP nor a reported non-caged borate-phosphine were

effective.

76

P

BX

L-X

Figure 2. A triptycene-type borate-phosphine (L-X).


Synthesis. The 9-phospha-10-boratriptycene framework was constructed following to the

synthetic route of the silicon-containing caged triarylphosphine TRIP derivatives, which was

originally reported by Tsuji and Tamao’s5 and modified by Sawamura.4 The route is

summarized in Scheme 1. Commercially available 1-bromo-2-iodobenzene (1) was converted

to tris(2-bromophenyl)phosphine (2) through the I–Mg exchange reaction followed by a

Cu-catalyzed reaction with PCl3. Three-fold Br–Li exchange reaction of 2 with tBuLi

followed by reaction with PhBF3K gave, after treatment with 1 M aq. HCl and purification by

silica gel column chromatography, a P-protonated borate-phosphine hybrid (L-H) in 72%

yield as an air- and moisture-stable solid. Deprotonation of L-H with Na2CO3 in MeCN gave

a sodium salt of free phosphine-borate (L-Na). The solubility of L-Na was good in

coordinating organic solvents such as THF, MeCN, acetone, and DMF, but poor with

non-polar hydrocarbon solvents such as toluene and hexane. The subsequent cation exchange

with nBu4NBr in MeCN/CH2Cl2 gave the corresponding tetrabutylammonium salt (L-NBu4),

which was also soluble in various organic solvents such as CH2Cl2, CHCl3, THF, MeCN,

acetone, and DMF. L-K and L-Cs could also be prepared by deprotonation of L-H with

K2CO3 or Cs2CO3 (Scheme 2). Free phosphines L-Na, L-K, L-Cs and L-NBu4 were

air-stable solids.

77

Scheme 1. Preparation of L-Na and L-NBu4.

P

B MeCN/CH2Cl2 (1:10), rt

2) PhBF3K (1 equiv) THF, –98 °C to rt3) 1M HCl aq

P

Br3

L-H 72%

Na

L-Na 91%

P

B

H

Na2CO3 (3 equiv)

MeCN, rt

L-NBu4 90%

I

Br

Bu4NBr (1 equiv)

2) PCl3 (1 equiv) CuI (10 mol%) –20 ºC to rt 2 63%1

(3.5 equiv)

P

B

NBu4

1) iPrMgBr (3.5 equiv) THF, –20 ºC

1) tBuLi (6 equiv) THF, –98 ºC

Scheme 2. Preparation of L-K and L-Cs

L-H 72%

P

B

HP

B

M

L-KL-Cs

M2CO3 (3 equiv)

MeCN, rt

M = K = Cs

78%91%

X-ray Crystal Structures. Single-crystal X-ray diffraction analysis of L-H, L-Na

(1,2-dimethoxyethane adduct) and L-NBu4 confirmed their triptycene structures with

bridgehead P and B atoms (Figure 3a-c). Comparison with the Si-analog Ph-TRIP indicated

that L-Na [1.836 Å (avg.) and 96.1° (avg.)] and L-NBu4 [1.831 Å (avg.) and 95.9° (avg.)]

had smaller P–C bond lengths and P–C–P angles than Ph-TRIP [1.845 Å (avg.) and 98.9°

(avg.)]. These changes were due to the smaller size of the B atom compared to the Si atom.

L-H had much shorter P–C bond lengths and larger C–P–C angles [1.778 Å (avg.) and 104.6°

(avg.)] than the other borate-phosphine hybrids.

78

(a) P

B

H

P–C length (ave.) 1.778 Å

C–P–C angle (ave.) 104.6°

(b) P

B

Na

O

O

OO

OO



(c)

P

B

N



Figure 3. ORTEP drawings of (a) L-H, (b) L-Na·3DME, and (c) L-NBu4 with thermal

ellipsoids drawn at the 30% probability level. Hydrogen atoms on the carbon atoms, except

for the hydrogen atom on phosphorous atom of L-H, are omitted for clarity.

79

Electron-donor Power of L-X Phosphine Ligands. To evaluate the electron-donating

ability of the borate-phosphine L-X as a phosphine ligand, a phosphine selenide (Se-L-NBu4)

of the tetrabutylammonium salt was prepared from L-NBu4 and Se by heating in CHCl3 at

60 °C, and its 1JP-Se coupling constant was measured by 31P NMR spectroscopy (Chart 1).12

Phosphine selenide Se-L-NBu4 has a smaller 1JP-Se coupling constant than the selenide of the

silicon-based phosphine selenide (Se-Ph-TRIP) (ΔJ = –74 Hz; Chart 1, top), indicating that the borate-phosphine is more basic. This borate effect in the caged system L was markedly

more significant than the reported borate effect in the non-caged phosphine

[PPh2(p-C6H4BPh3)][PPh4] (ΔJ = –28 Hz; Chart 1, bottom).10j,13

Chart 1. 1JP-Se Coupling Constants of Phosphine Selenides

Se-L-NBu4

P

B

NBu4

Se

1JP-Se = 719 HzSe-Ph-TRIP

P

Si

Se

1JP-Se = 793 Hz

PPh4

1JP-Se = 701 Hz 1JP-Se = 729 Hz

Ph2P BPh3

SePh3P Se

cf.

[Se-PPh2(p-C6H4BPh3)][PPh4]

ΔJ = –74 Hz

ΔJ = –28 Hz

A molecular electrostatic potential map of the DFT-optimized borate-phosphine L shows

that the boron-centered negative charge spreads out toward the four aromatic rings, and a

resulting increase in P-electron density is suggested by comparing the map with that of the

corresponding Si-based neutral phosphine Ph-TRIP (Figure 4).

80

(a) –150.462

–381.719 (kj/mol)

L

P

B

Mulliken Charge (P)–0.453

(b) 97.9651

–102.086 (kj/mol)

Ph-TRIP

P

Si

Mulliken Charge (P)–0.399

Figure 4. The molecular electrostatic potential map of (a) L and (b) Ph-TRIP

[Spartan’14, B3LYP/6-311+G(2df,2p)]

Transition Metal Complexes. The effects of the counter cation of L-X (X = Na and

NBu4) on metal coordination were investigated through the synthesis of Pd(II) complexes.

Specifically, the reaction between L-NBu4 and [PdCl(η3-allyl)]2 (P/Pd 1:1) in CH2Cl2 gave a

square-planar Pd(II) complex [PdCl(η3-allyl)(L-NBu4)] with a neutral metal center as an air-

and moisture-stable solid (Scheme 2 and Figure 5a). In contrast, the corresponding reaction

with L-Na in CH2Cl2 failed to produce a well-defined compound due to its decomposition

during the isolation process. However, when the reaction between L-Na and [PdCl(η3-allyl)]2

was conducted in a MeCN/CH2Cl2 mixed solvent system, a zwitterionic Pd complex

[Pd(η3-allyl)(MeCN)(L)] with a metal-centered positive formal charge was produced (Scheme 3 and Figure 5b). This complex could be isolated as a yellow-colored solid, but it

81

gradually decomposed in a CD2Cl2 solution to form Pd black and allylbenzene (detected by 1H NMR spectroscopy). The phenyl group of the allylbenzene should be derived from the

terminal phenyl substituent on the bridgehead B atom. Thus, this observation suggests that

the C–B bond in the B-phenyl group was cleaved upon transmetalation with the cationic Pd

center to form a Pd–Ph bond. The allylbenzene should be the product of reductive elimination

of the allyl and phenyl ligands on the Pd(II) center. Observation of a postulated neutral

9-phospha-10-boratriptycene or its Pd complex has so far been unsuccessful.

Scheme 2. Preparation of [PdCl(η3-allyl)(L-NBu4)]

P

B

Pd Cl

NBu4

[PdCl(η3-allyl)]2CH2Cl2, rt

[PdCl(η3-allyl)(L-NBu4)] 43% (after recrystallization)

(1 equiv Pd)+L-NBu4

Scheme 3. Preparation of [Pd(η3-allyl)(MeCN)(L)]

P

B

Pd NCMe

[PdCl(η3-allyl)]2MeCN/CH2Cl2, rt

[Pd(η3-allyl)(MeCN)(L)] 79%

(1 equiv Pd)+

–NaCl

L-Na

82

(a)

P

B

Pd

Cl

N

(b)

NPd

P

B

Figure 5. ORTEP drawings of (a) [PdCl(η3-allyl)(L-NBu4)] and (b)

[Pd(η3-allyl)(MeCN)(L)] with thermal ellipsoids drawn at the 30% and 50% probability level, respectively. For (a) hydrogen atoms on the carbon atoms are omitted for clarity. For (b),

hydrogen atoms on the carbon atoms, the disordered π-allyl group and a solvent molecule

MeCN are omitted for clarity.

Rhodium complexes were also synthesized by the reaction of L–X with [RhCl(cod)]2.

They showed similar reactivity by the change of counter cations. The reaction between

L-NBu4 and [RhCl(cod)]2 (P/Rh 1:1) in CH2Cl2 gave [RhCl(L-NBu4)(cod)] (Scheme 4,

Figure 6a). On the other hand, the reaction of L-Na and [RhCl(cod)]2 in the presence of

pyridine gave zwitterionic complex [Rh(L)(py)(cod)] (Scheme 5, Figure 6b).

Scheme 4. Preparation of [RhCl(L-NBu4)(cod)].

[RhCl(cod)]2CH2Cl2, rt

[RhCl(L-NBu4)(cod)] 60%

(1 equiv Rh)+L-NBu4

P

B

Rh Cl

NBu4

83

Scheme 5. Preparation of [Rh(L)(py)(cod)].

[RhCl(cod)]2 CH2Cl2, rt

[Rh(L)(py)(cod)] 99%

(1 equiv Rh)+

–NaCl

L-NaP

B

Rh Npyridine (10 equiv)

(a)

P

B

NCl

Rh

(b)

P

B

N

Rh

Figure 6. ORTEP drawings of (a) [RhCl(L-NBu4)(cod)] and (b) [Rh(L)(py)(cod)] with

thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms on the carbon atoms

are omitted for clarity.

Applications to Pd Catalysis. The synthetic utility of the borate-phosphine L was

demonstrated in the Pd-catalyzed Suzuki–Miyaura cross-coupling of aryl chlorides, for which

the effectiveness of bulky phosphines to produce catalytically active mono-P-ligated Pd

species has already been established.14 The efficiency of this reaction was influenced by the

electron-donating property of the ligand, favoring stronger electron-donor power, which is

demanded for cleavage of a C–Cl bond for oxidative addition to the Pd(0) center.15 We

envisaged that the borate-phosphine L might work favorably as a ligand for this

transformation for the following two reasons. First, multiple ligation of L might cause

electrostatic repulsion between the negative charges in the vicinity, resulting in favorable

mono-P-ligation. Second, the electron-donor power of the P lone pair of L is significantly

84

increased due to the negative charge as indicated by the NMR spectroscopy of Se-L-NBu4

and by the electrostatic potential analysis. To our delight, a homogeneous L-Pd system

appeared to be effective. Specifically, the coupling reaction between 1-butyl-4-chlorobenzene

(3a) and phenylboronic acid (4a) occurred with 2 mol% loading of a catalyst prepared in situ

from L-NBu4 and [PdCl2(PhCN)2] (P/Pd 2:1) in the presence of K3PO4 (3 equiv) at 60 °C in

DMF over 12 h, giving the cross-coupling product 5a in 92% yield (table 1, entry 1). The

anionic ligand (L-Na) with a sodium counter cation also produced an active catalyst (entry 4,

93%), comparable to that with L-NBu4. The effect of the P loading on the catalytic activity of

the L-NBu4-Pd system was significant (entry 2 and 3, 20% and 0%, respectively).

Other caged or non-caged phosphine ligands were used under the same conditions for

comparison (Table 1). Neutral triarylphosphines such as PPh3 (table 1, entry 5) and Ph-TRIP

(entry 6) induced almost no reaction, indicating the crucial importance of the borate moiety

of L. The previously reported PPh3-based non-caged borate-phosphine

[PPh2(p-C6H4BPh3)][PPh4] was completely ineffective (entry 7). This suggests the

importance of involving the borate group in the caged structure or at the position ortho to the

P atom.16 The ligand performance of the newly synthesized borate-phosphine L was

comparable to that of the silica-supported triptycene-type phosphine Silica-TRIP (in THF,

98%, entry 8)17 and the sterically bulky and electron-rich

(dicyclohexylphosphino)biphenyl-type ligand XPhos (93%, entry 9). The usefulness of the

former in the Suzuki–Miyaura coupling of aryl chlorides due to selective mono-P-ligation on

a silica gel surface was demonstrated in our previous study.4b

85

Table 1. Ligand Effects in the Pd-Catalyzed Coupling between 3a and 4aa

Ph(HO)2BnBu ClK3PO4 (3 equiv)DMF (1 mL), 60 ºC, 12 h4a (1.5 equiv)3a (0.2 mmol)

nBu Ph+

[PdCl2(PhCN)2] (2 mol%)Ligand (4 mol%)

5a (1H NMR yield)

entry ligand yield (%)b

1 L–NBu4 92 (92)

2 L–NBu4 (2 mol%, Pd:P 1:1) 20

3 L–NBu4 (6 mol%, Pd:P 1:3) 0

4 L-Na 93

5 PPh3 3

6 Ph-TRIP 2

7 [PPh2(p-C6H4BPh3)][PPh4] 0

8 Silica-TRIP (in THF) 98

9 XPhos 93 a Conditions: 3a (0.2 mmol), 4a (0.3 mmol), [PdCl2(PhCN)2] (2 mol%), ligand (4 mol%),

K3PO4 (0.6 mmol), DMF (1 mL), 60 °C, 12 h. b Yields are determined by 1H NMR analysis.

Isolated yields are in parentheses.

SiO2

OSiOO

O

P

SiOSiOO

O

SiMe3

Silica-TRIP

L-X

P

B

X

Ph-TRIP

P

Si

Ph4P

P

[PPh2(p-C6H4BPh3)][PPh4]

P

B

XPhos

86

The use of other solvent systems with L-NBu4 was tested (Table 2). Non- or

less-coordinating solvent such as toluene (0%) and 1,4-dioxane (0%) were ineffective due to

the low solubility of the catalyst. Other coordinating solvents such as THF (12%), MeCN

(12%) and MeOH (0%) were less effective than DMF.

Table 2. The effect of solvent on L-NBu4–Pd catalyzed Suzuki-Miyaura cross-coupling

between 3a and 4aa

entry solvent yield (%)b

1 DMF 92 (92)

2 toluene 0

3 1,4-dioxane 0

4 THF 12

5 MeCN 12

6 MeOH 0 a Conditions: 3a (0.2 mmol), 4a (0.3 mmol), [PdCl2(PhCN)2] (2 mol%), ligand (4 mol%),

K3PO4 (0.6 mmol), solvent (1 mL), 60 °C, 12 h. b Yields are determined by 1H NMR analysis.

Isolated yields are in parentheses.

The L-NBu4–Pd system (2 mol% Pd, P/Pd 2:1) catalyzed the cross-coupling between several

aryl chlorides and arylboronic acids (Chart 2). The reactions of 4-chloroanisole or methyl

4-chlorobenzoate with 4a proceeded smoothly at 60 °C, affording 5b and 5c in high yields.

The same conditions were applicable to the reaction of a sterically demanding

2-chlorotoluene, albeit with a moderate yield (5d). The reactions of 4-chlorotoluene with

4-methoxy- or 4-acetyl-substituted phenyboronic acids gave the corresponding coupling

products 5e and 5f, respectively, in good-to-high yields.

87

Chart 2. Suzuki–Miyaura Coupling Reactions between Aryl Chlorides (3) and Aryl Boronic

Acids (4)

(HO)2BClK3PO4 (3 equiv)DMF (1 mL), 60 ºC, 12 h4 (1.5 equiv)3 (0.2 mmol)

[PdCl2(PhCN)2] (2 mol%)L-NBu4 (4 mol%)

5

+R2 R2R1 R1

MeO

5b 85% 5c 98% 5d 64%

Me

5e 93%

Me OMe

5f 72%

MeO

Me

MeO

O

a Conditions: 3 (0.2 mmol), 4 (0.3 mmol), [PdCl2(PhCN)2] (2 mol%), L-NBu4 (4 mol%),

K3PO4 (0.6 mmol), DMF (1 mL), 60 °C, 12 h. Isolated yields are given.

3. Conclusion

Borate-containing caged triarylphosphines L-X, featuring a 9-phospha-10-boratriptycene

structure were developed. The coordination properties of L-X were dependent on the counter

cation. In the reaction with [PdCl(η3-allyl)]2, L-NBu4 provided the neutral Pd(II) complex

[PdCl(η3-allyl)(L-NBu4)], while L-Na in MeCN/CH2Cl2 gave the zwitterionic Pd(II)

complex [Pd(η3-allyl)(MeCN)(L)]. The borate-phosphines L-X were applicable to the

Pd-catalyzed Suzuki–Miyaura cross-coupling of aryl chlorides with arylboronic acids.


4.1. Instrumental and Chemicals

All reactions were carried out under nitrogen or argon atmosphere. Materials were

obtained from commercial suppliers or prepared according to standard procedures unless

otherwise noted. PhBF3K18, [PPh2(p-C6H4BPh3)][PPh4]10j, Silica-TRIP4b and Ph-TRIP4c were

prepared according to the reported procedure. Phenylboronic acid (4a),

4-methoxyphenylboronic acid (4b) and 4-acetylphenylboronic acid (4c) were recrystallized

from hot water or water/acetone before use.

NMR spectra were recorded on a JEOL ECX-II (400 MHz for 1H NMR, 100.5 MHz for 13C NMR, 128.3 MHz for 11B NMR, and 161.8 MHz for 31P NMR). 1H NMR and 13C NMR

chemical shift values are referenced to the residual solvent or Me4Si (1H; 0 ppm). 11B NMR

88

and 31P NMR chemical shift were referenced to BF3·OEt2 (11B, 0 ppm) and H3PO4 (31P; 0

ppm). High-resolution mass spectra (JEOL JMS-T100LP and Thermo Scientific Exactive for

ESI-HRMS) and elemental analysis (EAI CE-440) were recorded at the Instrumental

Analysis Division, Global Facility Center, Creative Research Institution, Hokkaido

University. IR spectra were measured with a PerkinElmer Frontier instrument. Melting points

were determined on a micro melting point apparatus using micro cover glass (Yanaco

MP-500D). TLC analyses were performed on commercial glass plates bearing 0.25-mm layer

of Merck Silica gel 60F254. Silica gel (Kanto Chemical Co., Ltd., Silica gel 60 N, spherical,

neutral) was used for column chromatography. GLC-analyses were conducted on a Shimadzu

GC-14B equipped with a flame ionization detector. DFT calculations

[B3LYP/6-311+G(2df,2p)] were performed with Spartan’16 v2.0.7 software (Wavefunction,

Inc.).


Preparation of 2. For the synthesis of 2, previously reported procedure4b was slightly

modified as follows. A mixture of 1-bromo-2-iodobenzene (39.6 g, 140 mmol,) in THF (140

mL) was cooled to –20 °C. A solution of iPrMgBr in THF (0.80 M, 175 mL, 140 mmol),

which was freshly prepared from 2-bromopropane and Mg, was added over 10 min to the

mixture. After stirring at –20 °C for 2 h, PCl3 (3.79 mL, 40 mmol) and CuI (762 mg, 4 mmol)

were added successively. The reaction mixture was allowed to warm gradually to room

temperature, and then stirred overnight. After quenching with NH4Cl aq., the reaction

mixture was extracted with EtOAc. The organic layer was washed with brine, dried over

MgSO4, filtered, and concentrated under reduced pressure. The residue was passed through a

short silica gel column with CH2Cl2 as an eluting solvent, and the volatiles was evaporated

under vacuum. The residual solids were recrystallized from toluene/MeOH to give

tris(2-bromophenyl)phosphine as a while solid (12.6 g, 63% yield). 1H NMR (400 MHz,

CDCl3): δ 6.74–6.77 (m, 3H), 7.22–7.28 (m, 6H), 7.63–7.66 (m, 3H). 13C NMR (100.5 MHz,

CDCl3): δ 127.77 (3C), 130.33 (d, JC–P = 34.5 Hz, 3C), 130.72 (3C), 133.16 (d, JC–P = 1.9 Hz,

3C), 134.67 (3C), 136.68 (d, JC–P = 11.5 Hz, 3C). 31P NMR (161.8 MHz, CDCl3): δ –2.8.

Preparation of L-H. A solution of tBuLi in pentane (1.64 M, 18.3 mL, 30 mmol) was

added over 30 min to a solution of 2 (2.50 g, 5.0 mmol) in THF (50 mL) at –98 °C. After

stirring for 1 h, PhBF3K (920 mg, 5.0 mmol) was added at –98 °C. The resulting mixture was

allowed to warm gradually to room temperature over 4 h. After treatment with 1M HCl aq,

the reaction mixture was extracted with EtOAc. The organic layer was washed with brine,

dried over MgSO4, filtered, and concentrated under reduced pressure. The crude product was

89

purified by silica gel column chromatography (hexane/CH2Cl2 100:0-to-0:100) followed by

recrystallization from CH2Cl2/hexane to give L-H as a white solid (1.26 g, 72% yield). Single

crystals of L-H suitable for X-ray diffraction studies were obtained by recrystallization from

CH2Cl2/hexane. M.p. 220 °C (decomp.). 1H NMR (400 MHz, CDCl3): δ 7.06 (tdd, J = 7.6, 4.8, 0.8 Hz, 3H), 7.22 (tt, J = 7.6, 1.2 Hz, 3H), 7.38 (tt, J = 7.6, 1.6 Hz, 1H), 7.54 (t, J = 7.6

Hz, 2H), 7.73 (dd, J = 15.2, 7.2 Hz, 3H), 7.81 (d, JP–H = 450 Hz, 1H), 7.82 (m, 3H), 8.08 (d, J

= 7.6 Hz, 2H). 13C NMR (100.5 MHz, CDCl3): δ 123.54 (d, JC–P = 15.4 Hz, 3C), 124.57, 124.64 (d, JC–P = 86.2 Hz, 3C), 127.39 (2C), 127.53 (d, JC–P = 12.4 Hz, 3C), 130.05 (3C),

132.92 (d, JC–P = 13.4 Hz, 3C), 135.99 (2C), 165.0–167.0 (m, 3C). One of signals for carbon

directly attached to boron atom was not observed. 31P NMR (161.8 MHz, CDCl3): δ –23.3

(partially relaxed 1:1:1:1 quartet, JP–B = ~20 Hz). 11B NMR (128.3 MHz, CDCl3): δ –9.2 (d,

JB–P = 23.4 Hz). IR (ATR): 3045.3, 1573.6, 1431.1, 1260.6, 1092.3, 889.2, 846.0, 816.0,

756.0, 706.1 cm–1. ESI-HRMS (m/z): [M–H]– calcd. for C24H1710BP, 346.12027; found,

346.12080. Elem. Anal. calcd for C24H18BP: C, 82.79; H, 5.21; found: C, 82.35; H, 5.17.

Preparation of L-Na. A mixture of L-H (174 mg, 0.5 mmol), finely grinded Na2CO3

(159 mg, 1.5 mmol) and MeCN (10 mL) was placed in a vial equipped with a magnetic

stirring bar. The mixture was stirred at room temperature for 6 h. The resulting mixture was

filtered through a pad of celite. The filtrate was concentrated to give pale yellow oil. The

crude product was redissolved in CH2Cl2/Et2O, and then evaporated. Repeating evaporation

was carried out to remove MeCN until the residue became amorphous solid. The residue was

washed with CH2Cl2/hexane to give L-Na as a white solid (167 mg, 91%). Single crystals of

L-Na·3DME suitable for X-ray diffraction studies were obtained by recrystallization from

DME/hexane. M.p. 316–319 °C. 1H NMR (400 MHz, acetone-d6): δ 6.68 (t, J = 7.2 Hz, 3H),

6.76 (t, J = 7.2 Hz, 3H), 7.13 (t, J = 7.2 Hz, 1H), 7.34 (t, J = 7.2 Hz, 2H), 7.50 (br-s, 3H),

7.56 (dd, J = 11.2, 7.2 Hz, 3H), 8.12 (br-s, 2H). 13C NMR (100.5 MHz, acetone-d6): δ 121.42 (d, JC–P = 14.4 Hz, 3C), 123.31, 125.45 (3C), 126.97 (2C), 131.72 (3C), 132.21 (d, JC–P =

43.1 Hz, 3C), 137.36 (2C), 147.08 (3C), 157.14 (q, JC–B = 57.6 Hz), 169.84 (q, JC–B = 44.0

Hz, 3C). 31P NMR (161.8 MHz, acetone-d6): δ –44.2. 11B NMR (128.3 MHz, acetone-d6): δ –7.4 (d, JB–P = 3.7 Hz). IR (ATR): 3045.6, 1574.0, 1426.2, 1256.4, 1186.7, 1024.6, 881.4,

747.4, 726.2, 689.2 cm–1. ESI-HRMS (m/z): [M–Na]– calcd. for C24H1710BP, 346.12027;

found, 346.12092. Elem. Anal. calcd for C24H17BNaP: C, 77.87; H, 4.63 found: C, 74.13; H,

4.47 (although these results are outside the range viewed as establishing analytical purity,

they are provided to illustrate the best values obtained to date).

Preparation of L-K. A mixture of L-H (69.6 mg, 0.2 mmol), K2CO3 (82.9 mg, 0.6

mmol) and MeCN (4 mL) was placed in a vial equipped with a magnetic stirring bar. The

90

mixture was stirred at room temperature for 6 h. The resulting mixture was filtered through a

pad of celite. The filtrate was concentrated to give pale yellow oil. The crude product was

redissolved in CH2Cl2/Et2O, and then evaporated. Repeating evaporation was carried out to

remove MeCN until the residue became amorphous solid. The residue was washed with

CH2Cl2/hexane to give L-K as a white solid (60.3 mg, 78%). M.p. decomp. (350 °C). 1H

NMR (400 MHz, acetone-d6): δ 6.67 (t, J = 7.2 Hz, 3H), 6.75 (t, J = 7.2 Hz, 3H), 7.12 (t, J = 6.8 Hz, 1H), 7.33 (t, J = 6.8 Hz, 2H), 7.50 (br-s, 3H), 7.55 (dd, J = 11.2, 7.2 Hz, 3H), 8.11

(br-s, 2H). 13C NMR (100.5 MHz, acetone-d6): δ 121.44 (d, JC–P = 15.3 Hz, 3C), 123.32,

125.47 (3C), 126.95 (2C), 131.73 (3C), 132.22 (d, JC–P = 44.1 Hz, 3C), 137.38 (2C), 147.10

(3C), 157.16 (q, JC–B = 57.5 Hz), 169.85 (q, JC–B = 44.1 Hz, 3C). 31P NMR (161.8 MHz,

acetone-d6): δ –44.2. 11B NMR (128.3 MHz, acetone-d6): δ –7.4 (d, JB–P = 3.6 Hz).

ESI-HRMS (m/z): [M–K]– calcd. for C24H1710BP, 346.12027; found, 346.12092.

Preparation of L-Cs. A mixture of L-H (69.6 mg, 0.2 mmol), Cs2CO3 (195.5 mg, 0.6

mmol) and MeCN (4 mL) was placed in a vial equipped with a magnetic stirring bar. The

mixture was stirred at room temperature for 6 h. The resulting mixture was filtered through a

pad of celite. The filtrate was concentrated to give pale yellow oil. The crude product was

redissolved in CH2Cl2/Et2O, and then evaporated. Repeating evaporation was carried out to

remove MeCN until the residue became amorphous solid. The residue was washed with

CH2Cl2/hexane to give L-Cs as a white solid (87.5 mg, 91%). M.p. decomp. (345 °C). 1H

NMR (400 MHz, acetone-d6): δ 6.74 (t, J = 7.2 Hz, 3H), 6.82 (t, J = 7.2 Hz, 3H), 7.17 (t, J =

7.2 Hz, 1H), 7.38 (t, J = 7.2 Hz, 2H), 7.53 (br-d, J = 7.2 Hz, 3H), 7.60 (dd, J = 10.8, 7.2 Hz,

3H), 8.10 (br-s, 2H). 13C NMR (100.5 MHz, acetone-d6): δ 120.94 (d, JC–P = 14.4 Hz, 3C), 122.70, 124.94 (3C), 126.30 (2C), 131.15 (3C), 131.74 (d, JC–P = 43.1 Hz, 3C), 136.55 (2C),

146.21 (3C), 155.97 (q, JC–B = 57.5 Hz), 168.96 (q, JC–B = 47.9 Hz, 3C). 31P NMR (161.8

MHz, acetone-d6): δ –44.6. 11B NMR (128.3 MHz, acetone-d6): δ –7.4 (d, JB–P = 3.7 Hz). ESI-HRMS (m/z): [M–K]– calcd. for C24H17

10BP, 346.12027; found, 346.12068.

Preparation of L-NBu4. To a solution of L-Na (74.0 mg, 0.2 mmol) in MeCN (400 µL)

and CH2Cl2 (4 mL) was added dropwise a solution of tetrabutylammonium bromide (64.5 mg,

0.2 mmol) in CH2Cl2 (1 mL). Upon addition, white precipitate was immediately formed.

After stirring for 1 h, the precipitate was filtered off. The filtrate was concentrated under

reduced pressure. Recrystallization of the residue from CH2Cl2/Et2O gave L-NBu4 as a white

solid (106 mg, 90%). M.p. 227–228 °C. 1H NMR (400 MHz, CDCl3): δ 0.60–0.75 (m, 8H),

0.88 (t, J = 7.2 Hz, 12H), 0.95–1.09 (m, 8H), 1.45–1.61 (m, 8H), 6.72 (t, J = 6.8 Hz, 3H),

6.80 (t, J = 6.8 Hz, 3H), 7.22 (t, J = 6.8 Hz, 1H), 7.38 (t, J = 6.8 Hz, 2H), 7.52 (d, J = 6.8 Hz,

3H), 7.57–7.63 (m, 3H), 8.06 (br-d, J = 6.8 Hz, 2H). 13C NMR (100.5 MHz, CDCl3): δ 13.80

91

(4C), 19.49 (4C), 23.66 (4C), 56.78 (4C), 121.30 (d, JC–P = 15.4 Hz, 3C), 123.04, 125.49 (3C),

126.28 (2C), 131.25 (3C), 131.99 (d, JC–P = 43.1 Hz, 3C), 136.60 (2C), 145.60 (3C), 168.85

(q, JC–B = 46.9 Hz, 3C). One of signals for carbon directly attached to boron atom was not

observed. 31P NMR (161.8 MHz, CDCl3): δ –45.2. 11B NMR (128.3 MHz, CDCl3): δ –8.6. IR (ATR): 2961.4, 2873.8, 1478.0, 1456.9, 1427.4, 1378.5, 1027.6, 878.4, 755.5, 737.3,

707.2, 688.2 cm–1. ESI-HRMS (m/z): [M–NBu4]– calcd. for C24H1710BP, 346.12027; found,

346.12086. Elem. Anal. calcd for C40H53BNP: C, 81.48; H, 9.06; N, 2.38; found: C, 81.52; H,

9.09; N, 2.39.

Preparation of Se-L-NBu4. A mixture of L-NBu4 (59.0 mg, 0.1 mmol), selenium (23.7

mg, 0.3 mmol) and CHCl3 (1 mL) was stirred at 60 °C for 3 h. The resulting mixture was

filtered through a pad of celite. Evaporation of volatiles gave Se-L-NBu4 as a white solid

(54.6 mg, 82%). M.p. 224–225 °C. 1H NMR (400 MHz, CDCl3): δ 0.80–1.07 (m, 28H), 1.98–2.12 (m, 8H), 6.86–6.98 (m, 6H), 7.29 (t, J = 7.2 Hz, 1H), 7.45 (t, J = 7.2 Hz, 2H),

7.56–7.63 (m, 3H), 7.98–8.08 (m, 5H). 13C NMR (100.5 MHz, CDCl3): δ 13.71 (4C), 19.41

(4C), 23.65 (4C), 57.51 (4C), 121.12 (d, JC–P = 14.3 Hz, 3C), 123.65, 126.69 (3C), 126.91

(2C), 127.69 (d, JC–P = 14.3 Hz, 3C), 130.80 (d, JC–P = 11.6 Hz, 3C), 135.79 (d, JC–P = 73.9

Hz, 3C), 136.35 (2C), 151.0–153.5 (m), 165.3–167.0 (m, 3C). 31P NMR (161.8 MHz,

CDCl3): δ 12.2 [partially relaxed 1:1:1:1 quartet, JP–B = ~25 Hz (satellite d, JP–Se = 719 Hz)]. 11B NMR (128.3 MHz, CDCl3): δ –10.6 (d, JB–P = 14.8 Hz). IR (ATR): 2962.2, 1429.4, 1254.2, 1058.0, 883.2, 761.7, 704.3 cm–1. ESI-HRMS (m/z): [M–NBu4]– calcd for

C24H17BPSe, 427.03316; found, 427.03421. Elem. Anal. calcd for C40H53BNPSe: C, 71.86;

H, 7.99; N, 2.09; found: C, 71.47; H, 8.01; N, 2.11.

Preparation of Se-Ph-TRIP. A mixture of Ph-TRIP (36.4 mg, 0.1 mmol), selenium

(23.7 mg, 0.3 mmol) and CHCl3 (1 mL) was stirred at 60 °C for 3 h. The resulting mixture

was filtered through a pad of celite. Evaporation of volatiles gave Se-Ph-TRIP as a white

solid (43.8 mg, 99%). M.p. 320–321 °C. 1H NMR (400 MHz, CDCl3): δ 7.32 (t, J = 7.2 Hz,

3H), 7.42 (tdd, J = 7.2, 3.2, 1.2 Hz, 3H), 7.70–7.81 (m, 6H), 8.27 (dd, J = 7.6, 1.6 Hz, 2H),

8.52 (dd, J = 15.6, 7.6 Hz, 3H). 13C NMR (100.5 MHz, CDCl3): δ 124.06, 128.45 (d, JC–P = 14.4 Hz, 3C), 129.01 (d, JC–P = 2.9 Hz, 3C), 129.19 (2C), 131.70 (d, JC–P = 14.4 Hz, 3C),

131.87, 132.07 (d, JC–P = 9.5 Hz, 3C), 136.45 (2C), 138.70 (d, JC–P = 71.0 Hz, 3C), 139.89 (d,

JC–P= 8.6 Hz, 3C). 31P NMR (161.8 MHz, CDCl3): δ 13.3 (satellite d, JP–Se = 793 Hz). IR (ATR): 2965.8, 1430.0, 1258.2, 1092.4, 883.9, 760.5, 736.3, 697.6, 667.7 cm–1. ESI-HRMS

(m/z): [M+H]+ calcd for C24H18PSeSi, 445.00751; found, 445.00888. Elem. Anal. calcd for

C24H17PSeSi: C, 65.01; H, 3.86; found: C, 64.15; H, 3.71. (although these results are outside

the range viewed as establishing analytical purity, they are provided to illustrate the best

92

values obtained to date).

Preparation of [PdCl(η3-allyl)(L-NBu4)]. A mixture of L-NBu4 (47.2 mg, 0.08 mmol),

[PdCl(η3-allyl)]2 (14.6 mg, 0.04 mmol) and CH2Cl2 (2 mL) was stirred at room temperature for 2 h. The volatiles were evaporated. The residue was recrystallized from CH2Cl2/Et2O to

give [PdCl(η3-allyl)(L-NBu4)] as a pale yellow solid (39.6 mg, 43% yield). Single crystals of

[PdCl(η3-allyl)(L-NBu4)] suitable for X-ray diffraction studies were obtained by recrystallization from CH2Cl2/hexane. M.p. 193 °C (decomp.). 1H NMR (400 MHz,

CD2Cl2): δ 0.93 (t, 7.2 Hz, 12H), 1.14–1.31 (m, 16H), 2.54–2.65 (m, 8H), 3.05 (d, J = 12.4

Hz, 1H), 3.91–4.02 (m, 2H), 4.86 (t, J = 6.8 Hz, 1H), 5.74–5.85 (m, 1H), 6.89 (td, J = 7.2, 3.2

Hz, 3H), 6.97 (t, J = 7.2 Hz, 3H), 7.27 (t, J = 7.2 Hz, 1H), 7.44 (t, J = 7.2 Hz, 2H), 7.56 (d, J

= 7.2 Hz, 3H), 8.04–8.12 (m, 5H). 13C NMR (100.5 MHz, CD2Cl2): δ 13.75 (4C), 19.94 (4C),

24.02 (4C), 55.24, 58.63 (4C), 82.17 (d, JC–P = 30.7 Hz), 116.60 (d, JC–P = 4.7 Hz), 122.02 (d,

JC–P = 17.4 Hz, 3C), 123.70, 126.71 (3C), 126.98 (2C), 131.38 (d, JC–P = 5.8 Hz, 3C), 132.41

(d, JC–P = 25.9 Hz, 3C), 136.83 (2C), 140.70 (d, JC–P = 43.1 Hz, 3C), 154.02 (q, JC–B = 60.4

Hz), 167.80 (q, JC–B = 45.9 Hz, 3C). 31P NMR (161.8 MHz, CD2Cl2): δ –6.8 (partially

relaxed 1:1:1:1 quartet, JP–B = ~15 Hz). 11B NMR (128.3 MHz, CD2Cl2): δ –9.3 (d, JB–P = 12.3 Hz). IR (ATR): 3040.0, 2961.7, 2872.1, 1485.8, 1427.5, 1381.7, 879.8, 756.4, 709.1,

695.3 cm–1. ESI-HRMS (m/z): [M–NBu4]– calcd for C27H22BClPPd, 529.02874; found,

529.02667. Elem. Anal. calcd for C43H58BClNPPd: C, 66.85; H, 7.57; N, 1.81; found: C,

66.62; H, 7.58; N, 1.80.

Preparation of [Pd(η3-allyl)(MeCN)(L)]. A mixture of L-Na (29.6 mg, 0.08 mmol),

[PdCl(η3-allyl)]2 (14.6 mg, 0.04 mmol), MeCN (1 mL) and CH2Cl2 (1 mL) was stirred at room temperature for 30 min. The pale-yellow suspension was filtered through a pad of celite.

The filtrate was concentrated to ca. 1 mL. White crystals formed upon concentration. The

crystals were collected by filtration to give [Pd(η3-allyl)(MeCN)(L)] acetonitrile monosolvate as a white solid (33.8 mg, 79% yield). Single crystals of

[Pd(η3-allyl)(MeCN)(L)]·(MeCN) suitable for X-ray diffraction studies were obtained by recrystallization from CH2Cl2/MeCN. M.p. 170 °C (decomp.). 1H NMR (400 MHz,

CD2Cl2/CD3CN = 10:1): δ 3.31 (br-s, 1H), 4.11 (dd, J = 14.0, 8.4 Hz, 1H), 4.33 (br-s, 1H),

5.24 (t, J = 6.8 Hz, 1H), 5.92 (m, 1H), 6.92 (tdd, J = 7.2, 3.2, 1.6 Hz, 3H), 7.01 (tt, J = 7.2,

1.2 Hz, 3H), 7.26 (t, J = 7.2 Hz, 1H), 7.44 (t, J = 7.2 Hz, 2H), 7.58 (br-d, J = 7.2 Hz, 3H),

7.67 (ddd, J = 9.6, 7.2, 1.2 Hz, 3H), 8.03 (br-d, J = 7.2 Hz, 2H). 13C NMR (100.5 MHz,

CD2Cl2/CD3CN = 10:1): δ 84.37 (d, JC–P = 24.0 Hz), 120.09, 122.33 (d, JC–P = 14.4 Hz, 3C), 123.84, 127.07 (2C), 127.29 (3C), 131.05 (d, JC–P = 24.9 Hz, 3C), 131.75 (d, JC–P = 7.6 Hz,

3C), 136.51 (2C), 138.65 (d, JC–P = 47.0 Hz, 3C), 167.50 (q, JC–B = 40.2 Hz, 3C). One of

93

signals for carbon directly attached to boron atom was not observed. Signals for one of

carbons of the π-allyl moiety and for carbons of the coordinating MeCN ligand were

overlapping to solvent signals. 31P NMR (161.8 MHz, CD2Cl2/CD3CN = 10:1): δ –3.2 (partially relaxed 1:1:1:1 quartet, JP–B = ~10 Hz). 11B NMR (128.3 MHz, CD2Cl2/CD3CN =

10:1): δ –9.2 (d, JB–P = 12.3 Hz). IR (ATR): 2964.6, 1428.0, 1255.0, 1025.8, 882.4, 756.2,

742.3, 719.8, 698.0 cm–1. ESI-HRMS (m/z): [M+Na]+ calcd. for C29H25BNPPd, 558.07656;

found, 558.07728. Elem. Anal. calcd for C31H28BN2PPd: C, 64.55; H, 4.89; N, 4.86; found:

C, 63.68; H, 4.78; N, 4.81. (although these results are outside the range viewed as

establishing analytical purity, they are provided to illustrate the best values obtained to date).

Preparation of [RhCl(L-NBu4)(cod)]. A mixture of L-NBu4 (23.6 mg, 0.04 mmol),

[RhCl(cod)]2 (9.9 mg, 0.02 mmol) and CH2Cl2 (1 mL) was stirred at room temperature for 15

min. The mixture was added Et2O (ca. 3 mL) to form yellow crystalline precipitate. The

crystals were collected by filtration to give [RhCl(L-NBu4)(cod)] (26.4 mg, 79% yield).

Single crystals of [RhCl(L-NBu4)(cod)] suitable for X-ray diffraction studies were obtained

by recrystallization from CH2Cl2/Et2O. M.p. 165 °C (decomp.). 1H NMR (400 MHz,

CD2Cl2): δ 0.93 (t, 7.2 Hz, 12H), 1.14–1.31 (m, 16H), 2.09–2.25 (m, 4H), 2.50–2.70 (m, 12H), 5.24 (br-s, 2H), 5.49 (br-s, 2H), 6.85 (td, J = 7.2, 1.2 Hz, 3H), 6.90 (t, J = 7.2 Hz, 3H),

7.23 (t, J = 7.2 Hz, 1H), 7.41 (t, J = 7.2 Hz, 2H), 7.47 (d, J = 6.8 Hz, 3H), 8.03 (d, J = 6.8 Hz,

2H), 8.03 (dd, J = 10.8, 6.8 Hz, 3H). 13C NMR (100.5 MHz, CD2Cl2): δ 13.74 (4C), 19.96 (4C), 24.06 (4C), 29.00 (2C), 34.33 (2C), 58.69 (4C), 67.22 (d, JC–Rh = 12.5 Hz, 2C) 101.74

(dd, JC–Rh = 12.5 Hz, JC–P = 7.6 Hz, 2C), 121.49 (d, JC–P = 13.5 Hz, 3C), 123.54, 126.08 (3C),

126.85 (2C), 130.84 (d, JC–P = 5.7 Hz, 3C), 133.48 (d, JC–P = 23.0 Hz, 3C), 136.94 (2C),

141.32 (d, JC–P = 41.2 Hz, 3C), 154.59 (q, JC–B = 61.3 Hz), 168.34 (q, JC–B = 45.0 Hz, 3C). 31P NMR (161.8 MHz, CD2Cl2): δ –1.73 (partially relaxed dq, JP–Rh = 143 Hz, JP–B = ~15

Hz). 11B NMR (128.3 MHz, CD2Cl2): δ –9.5 (d, JB–P = 11.2 Hz). ESI-HRMS (m/z): [M–NBu4]– calcd. for C32H29

10BClPRh, 592.08798; found, 592.08680.

Preparation of [Rh(L)(py)(cod)]. A mixture of L-Na (14.8 mg, 0.04 mmol),

[RhCl(cod)]2 (9.9 mg, 0.02 mmol), CH2Cl2 (1 mL) and pyridine (32.2 µL, 0.4 mmol) was

stirred at room temperature for 40 min. The resulting mixture was filtrated through a pad of

celite. The filtrate was concentrated under reduced pressure. The residue was recrystallized

from CH2Cl2/Et2O to give [Rh(L)(py)(cod)] as a yellow solid (22.0 mg, 98% yield). Single

crystals of [Rh(L)(py)(cod)] suitable for X-ray diffraction studies were obtained by

recrystallization from CH2Cl2/ Et2O. M.p. 210 °C (decomp.). 1H NMR (400 MHz, CD2Cl2):

δ 2.18–2.36 (m, 4H), 2.69–2.85 (m, 4H), 4.76 (s, 2H), 5.62 (s, 2H), 6.78–6.84 (m, 3H), 6.94 (t, J = 6.8 Hz, 3H), 7.20–7.28 (m, 3H) 7.42 (t, J = 6.8 Hz, 2H), 7.44 (t, J = 7.2 Hz, 3H), 7.61

94

(d, J = 7.6 Hz, 1H), 7.92 (dd, J = 11.6, 7.2 Hz, 3H), 7.61 (d, J = 7.2 Hz, 2H), 8.91 (d, J = 4.8

Hz, 2H). 13C NMR (100.5 MHz, CD2Cl2): δ 29.50 (2C), 33.16 (2C), 78.81 (d, JC–Rh = 11.5

Hz, 2C), 99.76 (2C), 121.9–122.2 (m, 5C), 123.88, 126.10 (3C), 127.14 (2C), 130.88 (d, JC–P

= 24.0 Hz, 3C), 132.01 (3C), 136.72 (2C), 138.33, 138.53 (d, JC–P = 41.6 Hz, 3C), 152.50.

signals for carbon directly attached to boron atom was not observed. 31P NMR (161.8 MHz,

CD2Cl2): δ –18.8 (partially relaxed dq, JP–Rh = 147 Hz, JP–B = ~15 Hz). 11B NMR (128.3

MHz, CD2Cl2): δ –9.4 (d, JB–P = 12.3 Hz). Attempts to obtain MS spectra (ESI or FAB) of [Rh(L)(py)(cod)] were unsuccessful.

Typical Procedure for Pd-Catalyzed Suzuki–Miyaura Cross-Coupling of Aryl

Chlorides. In a nitrogen-filled glove box, a mixture of L-NBu4 (4.7 mg, 0.008 mmol) and

DMF (850 µL) was placed in a 10 mL screw-capped glass tube containing magnetic stirring

bar. A solution of [PdCl2(PhCN)2] (1.5 mg, 0.004 mmol) in DMF (150 µL) was added to the

mixture. After stirring for 5 min, 1-butyl-4-chlorobenzene (3a, 33.5 mg, 0.20 mmol), phenylboronic acid (4a, 36.6 mg, 0.30 mmol), K3PO4 (127.4 mg, 0.6 mmol) were added

successively. The tube was sealed with a screw cap and removed from the glove box. The

mixture was stirred at 60 °C for 12 h. After cooling to room temperature, the consumption of

the starting material was determined by gas chromatography (1,4-dimethoxybenzene as

internal standard). The mixture was diluted with Et2O and filtered through a Celite pad

(eluting with Et2O). The volatiles were evaporated, and an internal standard

(1,3,5-trimethoxybenzene) was added to determine the yield of 4-butyl-1,1'-biphenyl (5a,

92% yield) by 1H NMR. The crude product was purified by silica gel chromatography

(hexane/EtOAc, 100:0-to-97:3) to give 5a as a colorless oil (0.20 mmol scale, 38.6 mg, 92%

yield). 1H NMR (400 MHz, CDCl3): δ 0.94 (t, J = 7.2 Hz, 3H), 1.33–1.44 (m, 2H), 1.59–1.68

(m, 2H), 2.64 (t, J = 7.6 Hz, 2H), 7.22–7.26 (m, 2H), 7.31 (t, J = 7.2 Hz, 1H), 7.41 (t, J = 7.2

Hz, 2H), 7.50 (d, J = 7.2 Hz, 2H), 7.55–7.60 (m, 2H). 13C NMR (100.5 MHz, CDCl3): δ 13.99, 22.41, 33.65, 35.28, 126.8–127.1 (m, 5C), 128.67 (2C), 128.81 (2C), 138.49, 141.14,

142.03. The synthesis of 5a was reported.19

4-Methoxy-1,1'-biphenyl (5b). The product 5b was isolated by silica gel

chromatography (hexane/EtOAc, 100:0-to-98:2) as a white solid (0.22 mmol scale, 33.9 mg,

85% yield). 1H NMR (400 MHz, CDCl3): δ 3.82 (s, 3H), 6.96 (d, J = 8.8 Hz, 2H), 7.29 (t, J =

7.2 Hz, 1H), 7.40 (t, J = 7.2 Hz, 2H), 7.50–7.56 (m, 4H). 13C NMR (100.5 MHz, CDCl3): δ 55.27, 114.13 (2C), 126.61, 126.69 (2C), 128.11 (2C), 128.69 (2C), 133.68, 140.75, 159.06.

The synthesis of 5b was reported.20

Methyl 4-phenylbenzoate (5c). The product 5c was isolated by silica gel

chromatography (hexane/CH2Cl2, 100:0-to-50:50) as a white solid (0.20 mmol scale, 42.1 mg,

95

98% yield). 1H NMR (400 MHz, CDCl3): δ 3.92 (s, 3H), 7.38 (t, J = 7.2 Hz, 1H), 7.45 (t, J =

7.2 Hz, 2H), 7.58–7.67 (m, 4H), 8.09 (d, J = 8.8 Hz, 2H). 13C NMR (100.5 MHz, CDCl3): δ

52.07, 126.96 (2C), 127.20 (2C), 128.07, 128.78, 128.85 (2C), 130.03 (2C), 139.88, 145.52,

166.91. The synthesis of 5c was reported.21

2-Methyl-1,1'-biphenyl (5d). The product 5d was isolated by silica gel chromatography

(hexane) and following GPC as a pale-yellow oil (0.20 mmol scale, 20.9 mg, 64% yield). 1H

NMR (400 MHz, CDCl3): δ 2.27 (d, 3H), 7.22–7.28 (m, 4H), 7.30–7.36 (m, 3H), 7.38–7.43

(m, 2H). 13C NMR (100.5 MHz, CDCl3): δ 20.47, 125.73, 126.71, 127.22, 128.01 (2C),

129.16 (2C), 129.78, 130.28, 135.31, 141.88, 141.91. The synthesis of 5d was reported.21

4-Methoxy-4'-methyl-1,1'-biphenyl (5e). The product 5e was isolated by silica gel

chromatography (hexane/CH2Cl2, 80:20) as a white solid (0.22 mmol scale, 39.9 mg, 93%

yield). 1H NMR (400 MHz, CDCl3): δ 2.37 (s, 3H), 3.81 (s, 3H), 6.94 (d, J = 8.0 Hz, 2H), 7.21 (d, J = 8.0 Hz, 2H), 7.44 (d, J = 8.0 Hz, 2H), 7.50 (d, J = 8.0 Hz, 2H). 13C NMR (100.5

MHz, CDCl3): δ 21.02, 55.25, 114.09 (2C), 126.52 (2C), 127.90 (2C), 129.40 (2C), 133.65,

136.29, 137.89, 158.85. The synthesis of 5e was reported.22

4-Acetyl-4'-methyl-1,1'-biphenyl (5f). The product 5f was isolated by silica gel

chromatography (hexane/CH2Cl2, 70:30-to-50:50) as a white solid (0.21 mmol scale, 31.3 mg,

72% yield). 1H NMR (400 MHz, CDCl3): δ 2.40 (s, 3H), 2.62 (s, 3H), 7.27 (d, J = 8.4 Hz, 2H), 7.52 (d, J = 8.4 Hz, 2H), 7.66 (d, J = 8.4 Hz, 2H), 8.01 (d, J = 8.4 Hz, 2H). 13C NMR

(100.5 MHz, CDCl3): δ 21.13, 26.61, 126.88 (2C), 127.04 (2C), 128.86 (2C), 129.63 (2C),

135.49, 136.85, 138.18, 145.63, 197.73. The synthesis of 5f was reported.23

4.3. X-ray crystallographic studies

Data were collected on a Rigaku Mercury 70 CCD diffractometer with graphite

monochromated Mo-Kα radiation (λ = 0.71075 Å, 50 kV, 200 mA), and processed using the

CrystalClear software.24 Structures were solved by a direct method using SIR-2011,25 and

refined by full-matrix least-square method using SHELXL-2014.26 Non-hydrogen atoms

were refined anisotropically. All hydrogen atoms were located on the calculated positions and

refined using a riding model. All calculations were performed using the CrystalStructure

software package.27

Crystal data for L-H (CCDC 1819398; recrystallization from CH2Cl2/hexane). Large

accessible voids, which may host disordered solvent molecules, remained in the crystal

structure. Thus, the SQUEEZE program in PLATON was employed for analysis.28 C24H18BP,

M = 348.19, triclinic, space group P-1 (#2), a = 10.6599(14) Å, b = 13.5205(18) Å, c =

96

14.248(2) Å, α = 83.895(6)°, β = 79.563(5)°, γ = 74.191(5)°, V = 1939.6(5) Å3, T = 170 K, Z = 4, density (calc.) = 1.192 g/cm3, total reflections collected = 14920, unique reflections =

7528 (Rint = 0.0242), R1 (I>2σ(I)) = 0.0389, wR2 (all data) = 0.1050, GOF = 1.064. A

response for the following B-level alert in the CIF validation reports is shown below.

PLAT910_ALERT_3_B Missing # of FCF Reflection(s) Below Theta(Min)

12Note

Response: Theta min = 3.099 deg. Data completeness (0.991) and R1 factor (0.0389)

were good enough for this structural assignment.

P

B

H

P–C length (ave.) 1.778 ÅC–P–C angle (ave.) 104.6°

Crystal data for L-Na·3DME (CCDC 1819399; recrystallization from

1,2-dimethoxyethane/hexane). C36H47BNaO6P, M = 640.54, monoclinic, space group P21/c

(#14), a = 13.304(3) Å, b = 11.724(2) Å, c = 24.602(5) Å, β = 105.224(3)°, V = 3702.7(13) Å3, T = 200 K, Z = 4, density (calc.) = 1.149 g/cm3, total reflections collected = 27766,

unique reflections = 7250 (Rint = 0.0407), R1 (I>2σ(I)) = 0.0583, wR2 (all data) = 0.1490,

GOF = 1.072. A response for the following B-level alert in the CIF validation reports is

shown below.


12Note




P

B

Na

O

O

OO

OO

97

Crystal data for L-NBu4 (CCDC 1819400; recrystallization from CH2Cl2/hexane).

C40H53BNP, M = 589.65, orthorhombic, space group Pbca (#61), a = 17.892(4) Å, b =

19.303(5) Å, c = 20.596(5) Å, V = 7113(3) Å3, T = 200 K, Z = 8, density (calc.) = 1.101

g/cm3, total reflections collected = 52557, unique reflections = 6979 (Rint = 0.0648), R1

(I>2σ(I)) = 0.0698, wR2 (all data) = 0.1612, GOF = 1.127. A response for the following

B-level alert in the CIF validation reports is shown below.


12Note



P

B

N


Crystal data for Ph-TRIP (CCDC 1819401; recrystallization from CH2Cl2/hexane).

C24H17PSi, M = 364.46, orthorhombic, space group Pnma (#62), a = 21.485(5) Å, b =

10.455(3) Å, c = 8.335(2) Å, V = 1872.3(8) Å3, T = 200 K, Z = 4, density (calc.) = 1.293

g/cm3, total reflections collected = 13732, unique reflections = 1946 (Rint = 0.0253), R1

(I>2σ(I)) = 0.0433, wR2 (all data) = 0.1184, GOF = 1.087. P

Si


98

Crystal data for [PdCl(η3-allyl)(L-NBu4)] (CCDC 1819402; recrystallization from

CH2Cl2/hexane). C43H40BClNPPd, M = 754.43, monoclinic, space group P21/n (#14), a =

16.363(5) Å, b = 14.574(5) Å, c = 17.970(6) Å, β = 111.162(4)°, V = 3996(2) Å3, T = 200 K, Z = 4, density (calc.) = 1.254 g/cm3, total reflections collected = 30036, unique reflections =

7825 (Rint = 0.0280), R1 (I>2σ(I)) = 0.0564, wR2 (all data) = 0.1591, GOF = 1.051. A

response for the following B-level alert in the CIF validation reports is shown below.


13Note



P

B

Pd

Cl

N

Crystal data for [Pd(η3-allyl)(MeCN)(L)] (CCDC 1819403; recrystallization from CH2Cl2/MeCN). C31H28BN2PPd, M = 576.76, orthorhombic, space group P212121 (#19), a =

10.6478(5) Å, b = 13.6696(8) Å, c = 18.2916(8) Å, V = 2662.4(2) Å3, T = 200 K, Z = 4,

density (calc.) = 1.439 g/cm3, total reflections collected = 20549, unique reflections = 5222

(Rint = 0.0197), R1 (I>2σ(I)) = 0.0222, wR2 (all data) = 0.0504, GOF = 1.048.

NPd

P

B

99

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Publication List (1) “Site-selective C–H Borylation of Quinolines at the C-8 Position Catalyzed by a

Silica-supported Phosphane-Iridium System.”

Konishi, S.; Kawamorita, S.; Iwai, T.; Steel, P. G.; Marder, T. B.; Sawamura, M.

Chem. Asian J. 2014, 9, 434–438.

(2) “Silica-supported Triptycene-type Phosphine. Synthesis, Characterization, and

Application to Pd-Catalyzed Suzuki–Miyaura Cross-coupling of Chloroarenes.”

Iwai, T.; Konishi, S.; Miyazaki, T.; Kawamorita, S.; Yokokawa, N.; Ohmiya, H.;

Sawamura, M. ACS Catal. 2015, 5, 7254–7264.

(3) “Synthesis, Properties and Catalytic Application of a Triptycene-Type

Borate-Phosphine Ligand.”

Konishi, S.; Iwai, T.; Sawamura, M. Organometallics 2018, in Press.

104

Acknowledgement

The study described in this thesis had been carried out under the direction of Professor

Masaya Sawamura at Graduate School of Chemical Sciences and Engineering, Hokkaido

University.

I would like to express my sincere gratitude to my supervisor, Professor Masaya

Sawamura for providing me this precious study opportunity, kind guidance, enormous

supports, insightful comments and invaluable discussion. I also wish to express my deepest

appreciation to Assistant Professor Tomohiro Iwai for his elaborated guidance, and

invaluable discussion, considerable encouragement and kind support. I am also very grateful

to Professor Hirohisa Ohmiya for his helpful discussions, considerable encouragement and

considerable suggestions. I wish to express my appreciation to Dr. Yohei Shimizu and Dr.

Fernando Arteaga Arteaga for helpful discussions and suggestions.

Professor Keiji Tanino, Professor Takanori Suzuki, Professor Takeshi Ohkuma gave me

insightful comment and considerate suggestions on this thesis.

Moreover, I am very grateful to my co-workers. I especially wish to express my deepest

appreciation to Dr. Soichiro Kawamorita for his elaborated guidance and supports. Mr.

Tatsuya Miyazaki and Ms. Natsumi Yokokawa made a significant contribution to the study

described in Chapter 2. I am also thankful to Dr. Kazunori Nagao, Dr. Tomoya Harada, Dr.

Ryo Murakami, Dr. Yurie Takayama, Dr. Kentaro Hohjoh, Mr. Takamichi Wakamatsu, Mr.

Ryotaro Tanaka and all other members in Prof. Sawamura’s group for the helpful discussions

and continuous encouragements.

Finally, I also like to express my gratitude to my family for their moral supports and

continuous assistance.

Shota Konishi

June, 2018

development of caged phosphine ligands for …...various pd catalysts capable of cross-coupling...

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